CN114269426A

CN114269426A - Ventricular sensing control in cardiac pacing systems

Info

Publication number: CN114269426A
Application number: CN202080058475.XA
Authority: CN
Inventors: M·E·莱巴格; J·曹; W·M·戴默; M·W·海茵克斯; J·E·赫德森; M·克梅雷尔; J·J·圣马丁; T·J·谢尔登
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2019-08-19
Filing date: 2020-08-19
Publication date: 2022-04-01
Also published as: US11786739B2; US20210052895A1; EP4017581A1; WO2021034880A1; US20230405332A1; EP4017581B1

Abstract

A medical device is configured to set a post-atrial time interval in response to an atrial event and to generate an event time signal in response to a ventricular electrical signal crossing an R-wave sensing threshold during the post-atrial time interval. In some examples, the device accumulates oversensing evidence in response to the event time signal and adjusts the ventricular sensing control parameter based on the accumulated oversensing evidence.

Description

Ventricular sensing control in cardiac pacing systems

Technical Field

The present disclosure relates to a medical device and method for controlling sensing of ventricular events based on oversensing evidence.

Background

During Normal Sinus Rhythm (NSR), the heart beat is modulated by electrical signals generated by the sino-atrial (SA) node located in the right atrial wall. Each atrial depolarization signal generated by the SA node spreads across the atria, causing depolarization and contraction of the atria, and reaches the Atrioventricular (AV) node. The AV node responds by propagating ventricular depolarization signals through the inter-ventricular His bundle, and thereafter responds to the bundle branches of the right and left ventricles and Purkinje (Purkinje) muscle fibers (sometimes referred to as the "His-Purkinje system").

Patients with conduction system abnormalities (e.g., poor AV node conduction, poor SA node function, or other conduction abnormalities) may house a pacemaker to restore a more normal heart rhythm and AV synchrony. Ventricular pacing may be performed to maintain a ventricular rate in a patient with atrioventricular conduction abnormalities. A single-chamber ventricular pacemaker may be coupled to a transvenous ventricular lead carrying an electrode placed in the right ventricle (e.g., in the right ventricular apex). The pacemaker itself is typically implanted in a subcutaneous pocket, where the transvenous ventricular lead is tunneled to the subcutaneous pocket. Intracardiac pacemakers have been introduced or proposed for full implantation within a patient's heart, thereby eliminating the need for transvenous leads. An intracardiac pacemaker may provide sensing and pacing from within a chamber of a patient's heart, such as from within the right ventricle of a patient having an AV conductive block.

A dual chamber pacemaker may be provided that includes a transvenous atrial lead carrying an electrode placed in the right atrium and a transvenous ventricular lead carrying an electrode placed in the right ventricle via the right atrium. Dual chamber pacemakers sense atrial and ventricular electrical signals and may provide both atrial and ventricular pacing as needed to promote normal atrial and ventricular rhythms and to promote AV synchrony when SA and/or AV nodes or other conduction abnormalities are present.

Ventricular pacing via electrodes at or near the apex of the right ventricle has been found to be associated with increased risk of atrial fibrillation and heart failure. Alternative pacing sites, such as pacing of the his bundle, have been studied or proposed. Cardiac pacing of the his bundle has been proposed to provide ventricular pacing along the natural conduction system of the heart. Pacing of the ventricle via the his bundle allows recruitment along the natural conduction system of the heart, including the purkinje fibers, and is hypothesized to promote more physiological normal cardiac activation than other pacing sites, such as the ventricular apex.

Disclosure of Invention

The technology of the present disclosure generally relates to controlling ventricular sensing in a medical device capable of pacing a heart. In some examples, the medical device is capable of delivering ventricular pacing pulses that may be delivered to the His bundle or along the His-Purkinje system. A medical device operating in accordance with the techniques disclosed herein detects evidence of oversensing through a ventricular channel of the medical device and adjusts a ventricular sensing control parameter in accordance with the oversensing evidence. Evidence of oversensing may relate to atrial event oversensing and/or cardiac potential signal oversensing. Ventricular sensing control parameters that may be adjusted are the post-atrial ventricular blanking period, the post-atrial safe pacing interval, and/or the ventricular sensitivity setting used to control the R-wave sensing threshold for sensing ventricular R-waves.

In one example, the present disclosure provides a medical device including sensing circuitry configured to sense a ventricular electrical signal, set an R-wave sensing threshold, set a post-atrial time interval in response to receiving an atrial event signal, and generate an event time signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval. The medical device further includes a control circuit configured to determine a count of event time signals generated by the sensing circuit and adjust the ventricular sensing control parameter based on the count of event time signals.

In another example, the present disclosure provides a method comprising sensing a ventricular electrical signal, setting an R-wave sensing threshold, receiving an atrial event signal, setting a post-atrial time interval in response to receiving the atrial event signal, and generating an event time signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval. The method includes determining a count of event time signals and adjusting a ventricular sensing control parameter based on the count of event time signals.

In yet another example, the present disclosure provides a non-transitory computer-readable storage medium storing a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to sense a ventricular electrical signal, set an R-wave sensing threshold, receive an atrial event signal, set a post-atrial time interval in response to receiving the atrial event signal, generate an event time signal in response to the atrial electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval, determine a count of the event time signal, and adjust a ventricular sensing control parameter based on the count of the event time signal.

The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims.

Drawings

Fig. 1 is a conceptual diagram of an Implantable Medical Device (IMD) system capable of pacing and sensing cardiac electrical signals of a patient's heart.

Fig. 2 is a conceptual diagram of the IMD of fig. 1 coupled to a ventricular lead advanced to an alternative ventricular sensing and pacing location.

Fig. 3 is a conceptual diagram of a leadless intracardiac pacemaker positioned within the right atrium for providing ventricular pacing through the his bundle.

Fig. 4 is a schematic diagram of circuitry that may be enclosed within an IMD configured to perform sensing and pacing using the techniques disclosed herein.

FIG. 5 is a schematic diagram of circuitry that may be included in a ventricular channel of the sensing circuit shown in FIG. 4.

Fig. 6 is a timing diagram illustrating signals that may be generated by the ventricular channels of fig. 5.

Fig. 7 is a flow chart of a method for accumulating evidence of oversensing and adjusting ventricular sensing control parameters that may be performed by a medical device.

Fig. 8 is a flow diagram of a method for accumulating evidence of oversensing and adjusting a ventricular sensing control parameter based on the accumulated evidence of oversensing according to another example.

Fig. 9 is a flow diagram of a method for controlling a ventricular sense control parameter based on oversensing evidence in the presence of atrial Arrhythmia (AT), according to an example.

Detailed Description

A medical device system capable of generating and delivering ventricular pacing pulses and sensing cardiac electrical signals is described herein. The ventricular electrode may also be relatively close to the atrial chamber when the ventricular electrode is positioned to sense ventricular signals and deliver pacing pulses to or near the his bundle. Thus, the cardiac electrical signals received by the ventricular sense electrodes may include a P-wave accompanied by intrinsic atrial depolarization, atrial pacing pulse artifact, and atrial evoked response signals following an atrial pacing pulse. Any of these atrial events present in the ventricular sense signal may be erroneously sensed by the medical device as an R-wave. Erroneously sensing an atrial event as an R-wave is referred to herein as "atrial event oversensing".

In some cases, an escherichia or bundle branch potential signal (referred to herein as a "cardiac potential signal"), which may precede the QRS waveform, may be present in the ventricular sensing signal, particularly when the sensing electrode is located near the his bundle or bundle branch. For example, when the amplitude of the escherichia beam potential signal (also referred to herein as an "H-wave") exceeds an R-wave sensing threshold, the H-wave may be erroneously over-sensed as an R-wave. Thus, the term "oversensing" as used herein may relate to oversensing of atrial events and/or potential signals of the heart produced by the His-Purkinje system prior to depolarization of the ventricular myocardium. For example, H-waves may occur between a true atrial event and a true R-wave. The H-waves following an atrial event may or may not follow the intrinsically conductive R-waves, depending on the presence of conductive blocks along the His-Purkinje system. Thus, in some cases, an oversensing H-wave or other cardiac potential signal produced by the His-Purkinje system may result in the retention of ventricular pacing pulses, which may lead to ventricular pauses or ventricular rhythm pauses when conductive blocks are present.

Techniques for accumulating evidence of oversensing are disclosed herein, which may or may not include actual oversensing resulting in sensing of a false R-wave and thus producing a false R-wave sense event signal. Accumulating the oversensing evidence may include determining a count of oversensing events, as described below. Oversensing events may be identified based on ventricular electrical signals crossing an R-wave sensing threshold during a post-atrial time interval. In response to an R-wave sensing threshold crossing identified as an oversensing event, an R-wave sensing event signal may or may not be generated. The R-wave sense event signal may or may not be generated depending on whether the sensing threshold crossing occurred during the post-atrial blanking interval. Thus, an oversensing event may or may not be an actual oversensing event.

A medical device as disclosed herein controls a ventricular sensing control parameter based on oversensing evidence to avoid or reduce the likelihood of erroneously sensing atrial events and/or cardiac potential signals as R-waves. Such oversensing may cause the medical device to hold ventricular pacing pulses, which may lead to ventricular progressions or ventricular rhythm pauses, which may reduce the benefit and effectiveness of pacing therapy or even cause patient symptoms. By using the techniques disclosed herein to control ventricular sense control parameters based on oversensing evidence, overall medical device performance is improved. The reliability and specificity of ventricular R-wave sensing is improved, and the effectiveness of subsequently delivered pacing therapies is improved, because suppressing or delivering ventricular pacing pulses is based on more reliable R-wave sensing.

Fig. 1 is a conceptual diagram of a medical device system 10 capable of pacing a heart 8 of a patient and sensing cardiac electrical signals. The system 10 includes an Implantable Medical Device (IMD) 14 coupled to a patient's heart 8 via transvenous medical electrical leads 16 and 18. IMD 14 is shown as a dual chamber device capable of delivering cardiac pacing pulses and sensing cardiac electrical signals in both the atrial and ventricular chambers. IMD housing 15 encloses internal circuitry corresponding to the various circuits and components described below in connection with fig. 4 for sensing cardiac signals from heart 8 and controlling electrical stimulation therapy, e.g., pacing therapy, delivered by IMD 14. In particular, circuitry enclosed by housing 15 controls ventricular sensing by adjusting one or more ventricular sensing control parameters in response to detecting atrial events of the his bundle or bundle branch and/or evidence of actual or possible oversensing of cardiac potential signals.

IMD 14 includes a connector block 12, and connector block 12 may be configured to receive proximal ends of atrial pacing and sensing leads 16 (hereinafter referred to as "atrial leads" 16) and ventricular pacing and sensing leads 18 (hereinafter referred to as "ventricular leads" 18). Each of

leads

16 and 18 is advanced transvenously for positioning electrodes for sensing and stimulation in the atria and ventricles, respectively. Atrial lead 16 may be positioned such that its distal end is located near the Right Atrium (RA) and the superior vena cava. Atrial lead 16 is equipped with pacing and sensing electrodes, shown as tip electrode 20 and ring electrode 22 spaced proximally from tip electrode 20.

Electrodes

20 and 22 provide sensing and pacing in the right atrium, and are each connected to a respective insulated conductor that extends within the elongated body of atrial lead 16. Each insulated conductor is coupled at its proximal end to a connector carried by the proximal lead connector 40 and thereby electrically coupled to internal IMD circuitry via the connector block 12.

As shown, ventricular lead 18 may be advanced within the right atrium to position

electrodes

32 and 34 for pacing and sensing near the his bundle according to the right atrial approach. The ventricular lead tip electrode 32 may be a helical electrode that may be advanced to the inferior end of the atrial septum, below the AV node, and near the tricuspid annulus to position the tip electrode 32 in or near the his bundle. A ring electrode 34 spaced proximally from the tip electrode 32 may serve as a return electrode with a cathode tip electrode 32 for pacing the right and left ventricles via the His-Purkinje system. While lead 18 is referred to herein as a ventricular pacing and sensing lead for delivering pacing pulses for pacing the ventricle, ventricular lead 18 may be referred to as a His-beam pacing and sensing lead when positioned for delivering pacing pulses to the ventricle via the His-Purkinje system. It should be appreciated that the locations of lead 18 and

electrodes

32 and 34 shown in fig. 1 are illustrative in nature, and that lead 18 and

electrodes

32 and 34 may be positioned for delivering pacing pulses to the his bundle, right and/or left bundle branches, Purkinje fibers, or anywhere along the natural conduction system of the heart to facilitate depolarization of the right and left ventricles via the natural conduction system of the heart. In other examples, ventricular lead 18 and

electrodes

32 and 34 may be positioned to deliver ventricular pacing pulses to the ventricular myocardium, e.g., along the ventricular septum or ventricular free wall. Thus, the

electrodes

32 and 34 are not limited to pacing and sensing at or near the His bundle as shown, but may be used to deliver ventricular pacing and sensing ventricular R-waves at other locations along the His-Purkinje system or along the ventricular myocardium.

Electrodes

32 and 34 are coupled to respective insulated conductors extending within the elongated body of ventricular lead 18, which provide electrical connection to a proximal lead connector 44 coupled to connector block 12 and thereby enable electrical connection to IMD circuitry enclosed by housing 15. Cardiac electrical signal sensing circuitry included in IMD 14 receives cardiac electrical signals from electrodes 32 and/or 34 of ventricular lead 18 to sense ventricular R-waves, as described below.

Electrodes

32 and 34 may be selected among bipolar ventricular sensing electrode vectors, or one electrode carried by ventricular lead 18 (e.g., tip electrode 32 or ring electrode 34) may be used in combination with housing 15 for receiving unipolar ventricular signals to sense R-waves by cardiac electrical signal sensing circuitry. Although atrial lead 16 and ventricular lead 18 are each shown to carry two electrodes, it is recognized that each lead may carry one or more electrodes for providing one or more selectable pacing and/or sensing electrode vectors, which may include a bipolar combination of electrodes carried by the respective lead or a unipolar combination of electrodes carried by the respective lead and IMD housing 15.

IMD 14 may be configured as a dual chamber pacemaker capable of sensing and pacing in an RA in an atrial-tracked ventricular pacing mode and sensing ventricular R-waves and delivering ventricular pacing pulses synchronized with the atrium. In other examples, IMD 14 may be coupled to a single lead advanced into the RA for sensing atrial and ventricular signals and delivering at least ventricular pacing pulses. IMD 14 may be a single chamber pacing device coupled only to ventricular lead 18, in which dual chambers sense both atrial and ventricular electrical signals and deliver pacing pulses to the ventricles to at least maintain a minimum ventricular rate and/or deliver ventricular pacing synchronized with the atrium. It should be appreciated that although IMD 14 is shown in fig. 1 as a pacemaker capable of delivering atrial and ventricular pacing, IMD 14 may be configured as an implantable cardioverter defibrillator capable of delivering both low voltage cardiac pacing therapy and high voltage cardioversion and defibrillation (CV/DF) shocks. In this case, IMD 14 may be coupled to at least one lead that carries at least one high voltage CV/DF electrode (e.g., an elongated coil electrode).

External device 50 is shown in telemetric communication with IMD 14 via communication link 60. External device 50 may include a processor 52, memory 53, a display unit 54, a user interface 56, and a telemetry unit 58. Processor 52 controls external device operation and processes data and signals received from IMD 14. Display unit 54, which may include a graphical user interface, displays data and other information to the user to view IMD operating and programming parameters and cardiac electrical signals retrieved from IMD 14. Data obtained from IMD 14 via communication link 60 may be displayed on display 54. For example, a clinician may view cardiac electrical signals received from IMD 14 and marker channel data and/or data derived therefrom. For example, processor 52 may generate a report of oversensing evidence accumulated by IMD 14 and any associated ventricular sensing control parameter adjustments based on the oversensing evidence for display to the user on display 54.

User interface 56 may include a mouse, touch screen, key pad, etc. to enable a user to interact with external device 50 to initiate a telemetry session with IMD 14 for retrieving data from IMD 14 and/or transmitting data to IMD 14, including programmable parameters for detecting evidence of oversensing and controlling ventricular sensing, as described herein. Telemetry unit 58 includes a transceiver and an antenna configured for bidirectional communication with telemetry circuitry included in IMD 14, and configured to operate in conjunction with processor 52 to transmit and receive data related to IMD function, which may include data related to oversensing detection or related data and automatic adjustment of ventricular sensing control parameters, via communication link 60.

May use a signal such as

A wireless Radio Frequency (RF) link of Wi-Fi or Medical Implant Communication Service (MICS) or other RF or Communication frequency bandwidth or Communication protocol establishes a Communication link 60 between IMD 14 and external device 50. Data stored or acquired by IMD 14, including physiological signals or associated data derived therefrom, results of device diagnostics, and history of detected rhythmic events and delivered therapies may be retrieved from IMD 14 by external device 50 following an interrogation command.

External device 50 may embody a programmer used in a hospital, clinic, or physician's office to retrieve data from IMD 14 and to program operating parameters and algorithms in IMD 14 to control IMD functions. The external device 50 may alternatively be embodied as a home monitor or a handheld device. External device 50 may be used to program cardiac signal sensing parameters, rhythm detection parameters, and therapy control parameters used by IMD 14. External device 50 may be used to program thresholds or other parameters for ventricular sensing and oversensing detection in accordance with the techniques disclosed herein into IMD 14.

Fig. 2 is a conceptual diagram of IMD 14 coupled to ventricular lead 18 advanced to an alternative ventricular sensing and pacing location. IMD 14 may be a dual chamber cardiac pacing device coupled to ventricular lead 18 and atrial lead 16. In this example, the distal portion of ventricular lead 18 is advanced within the RV for sensing ventricular electrical signals and delivering ventricular pacing pulses to the His bundle or His-Purkinje system according to the right ventricular approach.

Tip electrode 32 may be implanted in or along ventricular septum wall, for example, at a high level along the ventricular septum wall near the his bundle. The tip electrode 32 may be paired with a return anode ring electrode 34 for delivering ventricular pacing pulses to capture the native ventricular conduction system and/or ventricular myocardium and for sensing ventricular electrical signals including intrinsic R-waves and ventricular evoked response signals. In some examples, tip electrode 32 or ring electrode 34 may be paired with IMD housing 15 for unipolar sensing of ventricular signals.

When

electrodes

32 and 34 are in close proximity to the right atrium, for example, in the right atrial approach shown in fig. 1 or the right ventricular approach shown in fig. 2, ventricular sensing circuitry of IMD 14 may erroneously sense atrial events as R-waves. When the

electrodes

32 and 34 are located near the his bundle, the his bundle potential signal or H-wave may be erroneously sensed as an R-wave from the ventricular sense signal. The techniques disclosed herein enable IMD 14 to detect evidence of oversensing and/or evidence indicating that oversensing may occur when it occurs and take corrective action to reduce the likelihood of atrial events and/or H-wave (or beam branching potential) oversensing by adjusting ventricular sensing control parameters.

Fig. 3 is a conceptual diagram of a leadless intracardiac pacemaker 100 positioned within the RA for providing ventricular pacing via the his bundle. Pacemaker 100 may include a distal tip electrode 102 extending away from a distal end 112 of pacemaker housing 105. An intracardiac pacemaker 100 is shown implanted in the RA of the patient's heart 8 to place a distal tip electrode 102 to deliver pacing pulses to the his bundle. For example, the distal tip electrode 102 may be inserted at the lower end of the atrial septum, below the AV node, and near the tricuspid annulus to position the tip electrode 102 along, or near the his bundle. Distal tip electrode 102 may be a helical electrode that provides fixation to anchor pacemaker 100 at an implant location. In other examples, pacemaker 100 may include fixation members that include one or more prongs, hooks, barbs, spirals, or other fixation members that anchor the distal end of pacemaker 100 at the implant site.

A portion of the distal tip electrode 102 may be electrically insulated such that only a distal-most end of the tip electrode 102, furthest from the housing distal end 112, is exposed to provide targeted pacing at a tissue site that includes a portion of the his bundle. One or more housing-based electrodes 104 and 106 may be carried on a surface of the housing of pacemaker 100. Electrodes 104 and 106 are shown as ring electrodes that circumscribe the longitudinal sidewalls of pacemaker housing 105 extending from distal end 112 to proximal end 110. In other examples, a return anode electrode for sensing and pacing may be positioned on the housing proximal end 110. For example, pacing of the ventricle through the His-Purkinje system may be achieved using the distal tip electrode 102 as a cathode electrode and either of the housing-based electrodes 104 and 106 as a return anode.

Cardiac electrical signals produced by the heart 8 may be sensed by the pacemaker 100 using a sensing electrode pair selected from

electrodes

102, 104 and 106. For example, ventricular electrical signals for sensing ventricular R-waves may be sensed using distal tip electrode 112 and distal housing-based electrode 104. Electrodes 104 and 106 may be used to sense atrial electrical signals for sensing atrial P-waves. Atrial and ventricular electrical signals may be analyzed to sense atrial and ventricular events. In some examples, pacemaker 100 is a dual chamber pacemaker configured to deliver atrial pacing pulses using housing-based distal electrode 104 and proximal electrode 106, and to deliver ventricular pacing pulses through tip electrode 102 and proximal electrode 106. An example of a dual-chamber intracardiac pacemaker that may incorporate the techniques disclosed herein for controlling ventricular sensed parameters is generally disclosed in U.S. patent application publication No. 2019/0083800(Yang et al), which is incorporated herein by reference in its entirety.

The example IMD of fig. 1 and 2 and pacemaker 100 of fig. 3 are illustrative examples of medical devices configured to accumulate evidence of actual or possible oversensing of atrial events and/or cardiac potential signals as erroneous R-waves, and to control ventricular sensing, in accordance with the techniques disclosed herein. However, these techniques are not limited to the illustrative configurations of the sensing and pacing devices and associated electrodes shown in fig. 1-3. In various examples, a medical device configured to perform the techniques disclosed herein may include a leadless device with housing-based electrodes (as shown in fig. 3), a leadless pacemaker with an extension carrying one or more electrodes, or a medical device coupled to one or more medical electrical leads configured to position ventricular pacing and sensing electrodes. Such examples may include an external pacemaker coupled to one or more transcutaneous medical electrical leads.

Fig. 4 is a schematic diagram of circuitry that may be enclosed within an IMD configured to perform sensing and pacing using the techniques disclosed herein. The block diagram of fig. 4 represents IMD 14 (fig. 1 and 2) for purposes of illustration. It should be understood that the functionality attributed to the various circuits and components shown in fig. 4 for performing ventricular pacing and sensing by monitoring for oversensing evidence may be similarly implemented in the intracardiac pacemaker 100 of fig. 3 or other medical devices capable of delivering ventricular pacing pulses and sensing cardiac electrical signals.

Housing 15 is represented as an electrode in fig. 4 for use in cardiac electrical signal sensing, and in some instances, for delivering cardiac electrical stimulation pulses, such as unipolar pacing pulses. The electronic circuitry enclosed within housing 15 includes software, firmware, and/or hardware that cooperatively monitor cardiac electrical signals, determine when pacing therapy is needed, and deliver electrical pacing pulses to the patient's heart as needed according to programmed pacing modes and pacing pulse control parameters. The electronic circuitry includes control circuitry 80, memory 82, therapy delivery circuitry 84, sensing circuitry 86, telemetry circuitry 88, and power supply 98.

Power supply 98 provides power to the circuitry of IMD 14, including each of

circuits

80, 82, 84, 86, and 88 as needed. The power supply 98 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between the power supply 98 and each of the

other components

80, 82, 84, 86 and 88 should be understood from the general block diagram of fig. 4, but are not shown for clarity. For example, power source 98 may be coupled to one or more charging circuits included in therapy delivery circuit 84 for providing the power required to charge a holding capacitor included in therapy delivery circuit 84, which discharges at the appropriate time under the control of control circuit 80 to generate and deliver pacing pulses. The power supply 98 is also coupled to components of the sensing circuitry 86 (such as sense amplifiers, analog-to-digital converters, switching circuitry, etc.), the telemetry circuitry 88, and the memory 82 to provide power to the various circuits as needed.

The functional blocks shown in fig. 4 represent functionality included in IMD 14 and may include any discrete and/or integrated electronic circuit components used to implement analog and/or digital circuits capable of producing the functionality attributed herein to IMD 14 (or pacemaker 100). . The various components may include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, a state machine, or other suitable components or combinations of components that provide the described functionality. Given the disclosure herein, it is within the ability of one skilled in the art to provide software, hardware, and/or firmware to accomplish the described functionality in the context of any modern cardiac medical device system.

Control circuitry 80 communicates with therapy delivery circuitry 84 and sensing circuitry 86, e.g., via a data bus, for sensing cardiac electrical signals and scheduling delivery of cardiac electrical stimulation therapy in response to sensed cardiac events (e.g., P-waves attendant to atrial depolarization and R-waves attendant to ventricular depolarization, or absence). The available electrodes are electrically coupled to therapy delivery circuitry 84 for delivering electrical stimulation pulses to the patient's heart and/or sensing circuitry 86 for sensing cardiac electrical signals generated by the heart, which may include intrinsic signals (such as intrinsic P-waves and R-waves) generated by the heart in the absence of pacing pulses to capture the heart, and evoked response signals generated in response to pacing pulses of sufficient energy to cause capture.

The sensing circuitry 86 may include cardiac event detection circuitry that may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or other analog or digital components for detecting cardiac electrical events. Sensing circuitry 86 may include two or more sensing channels for detecting cardiac electrical events from two or more sensing electrode vectors. Sensing circuitry 86 may include switching circuitry for selectively coupling pairs of sensing electrodes from the available electrodes to atrial channel 87 and ventricular channel 89. The switching circuitry may include a switching array, switching matrix, multiplexer, or any other type of switching device suitable for selectively coupling components of sensing circuitry 86 to selected electrodes. For example, atrial signals may be received by atrial channel 87 via

electrodes

20 and 22 of atrial lead 16 (fig. 1), and ventricular signals may be received by ventricular channel 89 via

electrodes

32 and 34 of ventricular lead (fig. 1 and 2).

An atrial event detector may be included in atrial channel 87 for detecting intrinsic P-waves that accompany intrinsic atrial depolarization using one or both of

electrodes

20 and 22 carried by RA lead 16. A ventricular event detector may be included in ventricular channel 89 for detecting intrinsic R-waves attendant to intrinsic ventricular depolarization using one or both of

electrodes

32 and 34 carried by ventricular lead 18. Cardiac event sensing thresholds (such as P-wave sensing thresholds or R-wave sensing thresholds) may be automatically adjusted by sensing circuitry 86 under the control of control circuitry 80, e.g., based on timing intervals and sensing thresholds determined by control circuitry 80, stored in memory 82, and/or controlled by hardware, firmware, and/or software of control circuitry 80 and/or sensing circuitry 86. For example, the R-wave sensing threshold may be controlled after the ventricular blanking period to initiate a threshold voltage (which may be based on a previously sensed R-wave amplitude) and then reduced according to an attenuation curve until a minimum sensing threshold is reached. The minimum R-wave sensing threshold may be set to a programmed sensitivity setting for the ventricular channel. The sensitivity setting programmed to a voltage level typically in millivolts (e.g., in the range of 0.3 millivolts to 1.8 millivolts) is the lowest voltage level at which the ventricular channel senses R-waves when exceeded, which may be true R-waves or erroneously sensed R-waves, e.g., P-waves or H-waves due to an out-of-limit R-wave sensing threshold.

Upon detecting a cardiac electrical event based on a sensing threshold crossing, the sensing circuitry 86 may generate a sensed event signal that is communicated to the control circuitry 80. For example, atrial event detectors of atrial channel 87 may generate P-wave sensed event signals in response to P-wave sensing threshold violations occurring outside of any applied atrial blanking periods. The ventricular event detector of ventricular channel 89 may generate an R-wave sensed event signal in response to an R-wave sensing threshold violation. The sensed event signals generated by sensing circuitry 86 are used by control circuitry 80 to suppress scheduled pacing pulses and/or to set a pacing escape interval timer that controls the base time interval for scheduling cardiac pacing pulses.

As described below in connection with fig. 5, the ventricular channel may also include an oversensing event detector configured to detect when an R-wave sensing threshold crossing may occur during the post-atrial time interval. The post-atrial time interval may be initiated in response to a P-wave sensed event signal produced by atrial channel 87 or an atrial pacing pulse generated by therapy delivery circuitry 84. The time at which the R-wave sensing threshold during the post-atrial time interval is out-of-limit may be used by the control circuitry 80 to accumulate oversensing evidence even when the R-wave sensing threshold during the atrial event detector is not sensed by the ventricular event detector, e.g., due to the post-atrial ventricular blanking period, such that the sensing circuitry 86 does not generate an R-wave sensed event signal. In this manner and as described further below, the sensing circuitry 86 and control circuitry 80 are configured to cooperatively detect and accumulate evidence of possible oversensing, whether or not actual oversensing of atrial events or other events occurs, such as H-waves as false R-waves.

Each of the atrial channel 87 and ventricular channel 89 may also generate a respective digital Electrocardiogram (EGM) signal, which may be passed to the control circuit 80 for further processing and analysis. Each

channel

87 and 89 may include an input filter for receiving atrial or ventricular signals from a corresponding pair of sensing electrodes, a preamplifier, an analog-to-digital converter, and a band-pass, low-pass, or high-pass filter for generating a multi-bit digital EGM signal that may be passed to control circuit 80. In some instances, the control circuit 80 may analyze the ventricular EGM signal to accumulate oversensing evidence. The control circuit 80 may determine ventricular signal characteristics, such as maximum peak signal amplitude, time of maximum peak, and/or R-wave sensing threshold crossing time, during the post-atrial time interval based on signals received from the oversensing event detectors of the ventricular channel 89 and/or by processing and analyzing ventricular EGM signals received from the ventricular channel 89. The control circuit 80 may use such ventricular signal characteristics to accumulate oversensing evidence and control ventricular sense control parameters based on the evidence.

Control circuit 80 may include various timers or counters for counting various pacing escape intervals, such as Atrioventricular (AV) pacing intervals, VV pacing intervals, AA pacing intervals, and the like. The sensed event signals may trigger or inhibit a pacing pulse depending on the particular programmed pacing mode. For example, a P-wave sensed event signal received from sensing circuitry 86 may cause control circuitry 80 to suppress scheduled atrial pacing pulses and schedule ventricular pacing pulses at a programmed AV pacing interval. If the AV pacing interval expires before control circuitry 80 receives the R-wave sensed event signal from sensing circuitry 86, control circuitry 80 may control therapy delivery circuitry 84 to deliver a ventricular pacing pulse at the AV pacing interval following the sensed P-wave, and in this manner deliver ventricular pacing synchronized with the atrium. If an R-wave sensed event signal is received from sensing circuitry 86 before the AV pacing interval expires, the scheduled ventricular pacing pulse may be suppressed. The AV pacing interval controls the amount of time between a paced or sensed atrial event and a ventricular pacing pulse to facilitate AV synchronization in an atrial tracking ventricular pacing mode. However, when an event, which may be an atrial pacing pulse artifact, an atrial-evoked response signal, an intrinsic P-wave, or an H-wave, is oversensively sensed by the ventricular event detector of ventricular channel 89 as a false-error R-wave, the ventricular pacing pulse may be suppressed, resulting in a pacemaker-dependent patient ventricular pause or ventricular arrest.

Accordingly, the control circuit 80 is configured to accumulate actual and/or possible oversensing evidence using the techniques disclosed herein for controlling R-wave sensing through the ventricular channel 89 in a manner that avoids or minimizes the likelihood of actually oversensing atrial events and/or cardiac potential signals as false R-waves. For example, control circuitry 80 may include a counter for counting event time signals generated by sensing circuitry 86 that correspond to R-wave sensing threshold violations during post-atrial time intervals. As described further below, the event time signal may be generated by an oversensing event detector included in the sensing circuit 86. By counting at least the number of event time signals generated during the post-atrial time interval (e.g., during a predetermined number of ventricular cycles of movement), oversensing evidence may be accumulated by the control circuitry 80.

A medical device configured to perform the techniques disclosed herein may be configured to deliver ventricular tachycardia pacing therapy, atrial synchronized ventricular pacing, rate-responsive pacing, Cardiac Resynchronization Therapy (CRT), anti-tachycardia pacing therapy, or other pacing therapies that may include pacing a ventricle, e.g., via the His-Purkinje system or any portion thereof. Therapy delivery circuitry 84 may include charging circuitry, one or more charge storage devices, such as one or more holding capacitors, an output capacitor, and switching circuitry that controls delivery of pacing pulses to selected pacing electrode vectors connected to therapy delivery circuitry 84 when the holding capacitors are charged and discharged across the output capacitor. Therapy delivery circuitry 84 may include one or more pacing channels. In the example of IMD 14, therapy delivery circuitry 84 may include an atrial pacing channel and a ventricular pacing channel. Each pacing channel may include one or more holding capacitors, one or more switches, and an output signal line, which may include at least one output capacitor, for producing pacing pulses delivered by the respective atrial lead 16 (electrodes 20 and 22) or ventricular lead 18 (electrodes 32 and 34). Charging the holding capacitor to the programmed pacing voltage amplitude and discharging the capacitor for the programmed pacing pulse width may be performed by therapy delivery circuit 84 in accordance with control signals received from control circuit 80. For example, the pacing timing circuitry included in the control circuitry 80 may include programmable digital counters set by the microprocessor of the control circuitry 80 for controlling the basic pacing time intervals associated with various single or dual chamber pacing modes, CRT, or anti-tachycardia pacing sequences. The microprocessor of the control circuit 80 may also set the amplitude, pulse width, polarity, or other characteristic of the cardiac pacing pulses, which may be based on programmed values stored in the memory 82.

In some examples, IMD 14 may be configured to detect non-sinus tachycardia and deliver anti-tachycardia pacing (ATP). The control circuitry 80 may determine cardiac event time intervals, such as PP intervals between successive P-wave sensed event signals received from the sensing circuitry 86 and/or RR intervals between successive R-wave sensed event signals received from the sensing circuitry 86. These intervals may be compared to tachycardia detection intervals to detect non-sinus tachycardias. Tachycardia can be detected in a given heart chamber based on a threshold number of tachycardia detection intervals that are detected. In response to detecting atrial or ventricular tachycardia, the control circuitry 80 may control the therapy delivery circuitry 84 to deliver ATP.

In some examples, therapy delivery circuitry 84 may include high voltage therapy circuitry for generating high voltage shock pulses in addition to low voltage therapy circuitry for generating low voltage pacing pulses. In response to detecting atrial or ventricular tachycardia or fibrillation, the control circuitry 80 may control the therapy delivery circuitry 84 to deliver a cardioversion/defibrillation (CV/DF) shock. The high voltage therapy circuitry may include high voltage capacitors and high voltage charging circuitry for generating and delivering CV/DF impact pulses.

Control parameters used by control circuitry 80 to sense cardiac events and control pacing therapy delivery may be programmed into memory 82 via telemetry circuitry 88. Telemetry circuitry 88 includes a transceiver and antenna for communicating with external device 50 using radio frequency communication or other communication protocols, as described above in connection with fig. 1. Under the control of control circuitry 80, telemetry circuitry 88 may receive downlink telemetry from external device 50 and transmit uplink telemetry to external device 50. In some cases, the telemetry circuitry 88 may be used to transmit and receive communication signals to another medical device implanted in the patient.

FIG. 5 is a conceptual diagram of circuitry that may be included in ventricular channel 89 of sensing circuit 86 shown in FIG. 4. In this example, ventricular channel 89 includes a prefilter/amplifier 172, an analog-to-digital converter (ADC)174, a rectifier/amplifier 175, and a ventricular event detector 176. The pre-filter amplifier circuit 172 receives ventricular signals from the ventricular pace and sense electrodes 32 and 34 (or from one of the

electrodes

32 or 34 paired with the housing 15). It should be appreciated that in other configurations, other available electrodes may be selected to receive ventricular electrical signals generated by the patient's heart. The pre-filter/amplifier circuit 172 may include a low pass filter for filtering out high frequency noise or artifacts and amplifies the filtered signal, which is passed to the ADC 174. The ADC 174 passes the digitized signal to a rectifier/amplifier circuit 175, which rectifier/amplifier circuit 175 may include a rectifier, band pass filter, and/or amplifier for passing the rectified signal to a ventricular event detector 176.

Ventricular event detector 176 may include a comparator, sense amplifier, or other detection circuitry configured to detect an R-wave sensing threshold violation by a ventricular signal. In response to the R-wave sensing threshold crossing, ventricular event detector 176 generates an R-wave sensed event signal 178 that is output to control circuitry 80. Ventricular event detector 176 may receive blanking signal 177, which may be controlled by a timer in sensing circuitry 86 or control circuitry 80, and set according to a sensed control parameter received from control circuitry 80. As described below, the control circuit 80 may enable a post-atrial ventricular blanking period in response to accumulating evidence of oversensing in order to reduce the likelihood of oversensing atrial events and/or cardiac potential signals of the his bundle or bundle branch. For example, ventricular event detector 176 may apply a post-atrial blanking interval to the ventricular signal received from rectifier/amplifier 175 to prevent ventricular event detector 176 from generating R-wave sensed event signals 178 during the post-atrial ventricular blanking interval. Ventricular event detector 176 is prevented from generating false R-wave sensed event signals based on R-wave sensing threshold violations that may occur during the post-atrial ventricular blanking. In other examples, the post-atrial blanking period may be applied by control circuitry 80 to ignore any R-wave sensed event signals generated by ventricular event detector 176 and received during the post-atrial blanking period.

Blanking signal 177 may be provided to blank the start time and duration or end time of ventricular event detector 176 during a blanking period that is enabled in response to a sensed or paced atrial event. In some examples, blanking signal 177 received by event detector 176 or, more generally, ventricular channel 89 may include a plurality of blanking signals applied to one or more components of ventricular channel 89 such that event detector 176 is effectively disabled from sensing events during the post-atrial blanking and re-enabled to sense events after the post-atrial blanking period terminates. In various instances, the blanking period may be imposed by temporarily disabling or disconnecting circuitry of ventricular channel 89 during the post-atrial ventricular blanking period or otherwise inhibiting event detector 176 from generating R-wave sensed event signals.

In some examples, ventricular channel 89 may include an oversensing event detector 180, which may include a comparator, sense amplifier, or other detection circuit that detects an R-wave sensing threshold violation of a ventricular signal received from rectifier/amplifier 175. The oversensing event detector 180 may receive an input from the rectifier amplifier circuit 175. Oversensing event detector 180 may include the same or similar circuitry as ventricular event detector 176 configured to detect an R-wave sensing threshold violation. In other examples, the oversensing event detector 180 may receive input from the ADC 174 and include a rectifier/amplifier circuit, which may be the same as or similar to the rectifier/amplifier circuit 175. In various examples, the input to the oversensing event detector 180 may be received directly from the

electrodes

32 and 34, or from any point in the pre-filter/amplifier 172, ADC 174, rectifier/amplifier circuit 175, or ventricular event detector 176. Accordingly, the oversensing event detector 180 may include circuitry for filtering, amplifying, digitizing and/or rectifying according to the input source. One or both of ventricular event detector 176 or oversensing event detector 180 may include peak amplitude detector circuitry for detecting the peak amplitude and/or time of peak amplitude of a cardiac electrical signal event that crosses a corresponding R-wave sensing threshold.

However, when the post-atrial ventricular blanking period is enabled and applied by the ventricular event detector 176 (or the control circuit 80), the oversensing event detector 180 does not apply the post-atrial ventricular blanking period. Conversely, oversensing event detector 180 may be enabled to sense R-wave sensing threshold violations that occur during the post-atrial ventricular blanking. However, the oversensing event detector 180 does not generate an R-wave sensed event signal in response to the R-wave sensing threshold crossing. Conversely, the oversensing event detector 180 may communicate an event time signal 186, and in at least some instances, an event peak amplitude signal 188 determined from the event signal that violates the R-wave sensing threshold to the control circuit 80.

In some examples, the oversensing event detector 180 may generate an event time signal 186 corresponding to an R-wave sensing threshold violation, where the event time signal 186 coincides with a detected time of the R-wave sensing threshold violation. Additionally or alternatively, the oversensing event detector 180 may generate an event time signal that coincides with the time of the peak amplitude of the event signal that crosses the R-wave sensing threshold. The event time signal that coincides with the peak amplitude corresponding to the R-wave sensing threshold is shown in fig. 5 as peak time signal 187. The peak time signal 187 may be the time of the maximum peak amplitude of the rectified cardiac electrical signal detected during the post-atrial time interval. The maximum peak amplitude may be detected after the R-wave sensing threshold is out-of-limit during the post-atrial time interval. The post-atrial time interval may be the same or different than the post-atrial ventricular blanking period imposed by the event detector 176.

In various examples described herein, one or both of the event time signal 186 and the peak time signal 187 may be passed to the control circuit 80. The control circuit 80 accumulates evidence of oversensing based on the event time signal 186, the peak time signal 187, and/or the event amplitude signal 188. In other examples, the control circuit 80 may receive digitized ventricular EGM signals 185 from the ventricular channel 89 and process and analyze the EGM signals 185 for detecting and determining oversensing evidence, such as for R-wave sensing threshold crossing times after an atrial event and/or maximum peak amplitudes and peak times of the EGM signals after the atrial event or event time signal 186.

In some examples, oversensing event detector 180 may receive P-wave sensed event signals 183 from atrial channel 87 indicating the timing of the sensed P-waves. Alternatively, atrial channel 87 may pass the P-wave sensed event signals to control circuitry 80 at each crossing of the P-wave sensing threshold, and control circuitry 80 may pass the P-wave sensed event signals 183 to oversensing event detector 180. Oversensing event detector 180 may additionally receive an atrial pacing signal 184 (either from therapy delivery circuitry 84 or from control circuitry 80), the atrial pacing signal 184 indicating the time of the atrial pacing pulse generated and delivered by therapy delivery circuitry 84. Oversensing event detector 180 may be configured to detect when an R-wave sensing threshold violation of a ventricular signal occurs during a post-atrial time interval extending from a P-wave sensed event signal or extending from an atrial pacing pulse. The post-atrial time interval may correspond to a post-atrial ventricular blanking period that may be applied by ventricular event detector 176. In other examples, the post-atrial time interval may be a programmable time interval that may begin and/or end at a time other than the post-atrial ventricular blanking period. For example, the post-atrial time interval may be longer than the post-atrial ventricular blanking period. As an example, the post-atrial ventricular blanking period may be set to 80 milliseconds (ms) and the post-atrial time interval may be set to 120 ms. The oversensing event detector 180 may be enabled to detect R-wave sensing threshold violations only during the post-atrial time interval in order to generate an event time signal 186 (and/or a peak time signal 187 and/or an event peak amplitude signal 188) that is received by the control circuit 80 for accumulating evidence of oversensing.

In this way, oversensing evidence indicating the likelihood of erroneously sensing atrial events and/or cardiac potential signals by ventricular event detector 176 may be accumulated even when erroneous R-wave sensed event signals are not generated by ventricular event detector 176. For example, an R-wave sensing threshold violation may be detected by oversensing event detector 180 during the overlapping portion of the post-atrial time interval and the post-atrial ventricular blanking period. Oversensing event detector 180 may generate event time signal 186 instead of R-wave sensed event signal 178 generated by ventricular event detector 176. Evidence of oversensing may be increased based on the event time signal 186 without the atrial event or cardiac potential signal actually being oversensing by the ventricular event detector 176 or used by the control circuit 80 to inhibit ventricular pacing pulses.

When the R-wave sensing threshold is set to the same magnitude (which may decay over time) as the R-wave sensing threshold used by ventricular event detector 176, oversensing event detector 180 may be controlled to detect an R-wave sensing threshold violation of the cardiac electrical signal. In this manner, the oversensing event detector 180 may identify events that will be sensed by the ventricular event detector 176 when the ventricular event detector 176 is disabled. However, in other examples, when the R-wave sensing threshold is set differently (e.g., higher or lower) than the R-wave sensing threshold applied by ventricular event detector 176, oversensing event detector 180 may be controlled to detect the R-wave sensing threshold violation. For example, oversensing event detector 180 may be set to different amplitudes to determine the frequency of sensed (or not sensed) events using a different R-wave sensing threshold than ventricular event detector 176. For example, when the R-wave sensing threshold applied by the oversensing event detector 180 is lower than the R-wave sensing threshold applied by the ventricular event detector 176, the control circuit 80 may determine, by the ventricular event detector 176, the likelihood of oversensing events during the post-atrial time interval if the R-wave sensing threshold decreases. The control circuit 80 may adjust the R-wave sensing threshold used by the oversensing event detector 180 to be different from the R-wave sensing threshold temporarily applied by the ventricular event detector 176 to test possible ventricular sensing control parameters, such as sensitivity settings, in order to predict whether oversensing is expected to occur before actually adjusting the ventricular sensing control parameters.

Fig. 6 is a timing diagram 150 illustrating signals that may be generated by ventricular event detector 176 and oversensing event detector 180 of fig. 5. Atrial event signal 152 may be received by ventricular channel 89 for setting a post-atrial blanking period 160 (when blanking is enabled) applied by ventricular event detector 176 and a post-atrial time interval 162 applied by oversensing event detector 180. Atrial event signal 152 may correspond to an intrinsic P-wave sensed by sensing circuitry 86 or an atrial pacing pulse generated by therapy delivery circuitry 84.

Ventricular signal 153 represents the rectified signal passed from rectifier/amplifier 175 to ventricular event detector 176 and oversensing event detector 180. Ventricular signals 153 include early event signals 154 and late event signals 156. Early event signal 154 occurring within post-atrial time interval 162 may be an atrial event signal corresponding to atrial event 152 that may be over-sensed by ventricular event detector 176 if post-atrial ventricular blanking period 160 is disabled. If the blanking period 160 is disabled, ventricular event detector 176 may generate a false R-wave sensed event signal 166 that may cause therapy delivery circuitry 84 to suppress the ventricular pacing pulse. However, when the post-atrial ventricular blanking 160 is enabled, any R-wave sensing threshold violations that occur by the ventricular event detector 176 during the post-atrial ventricular blanking period 160 are ignored, such that R-wave sensed event signals are not generated. In other examples, ventricular event detector 176 may generate R-wave sensed event signals 166 during blanking period 160, but control circuit 80 applies blanking period 160 and ignores any R-wave sensed event signals received during blanking period 160 in order to control ventricular pacing (e.g., without inhibiting or scheduling ventricular pacing pulses based on R-wave sensed event signals 166).

The oversensing event detector 180 is enabled to detect an R-wave sensing threshold violation during the post-atrial time interval 162. After expiration of the post-atrial time interval 162, the oversensing event detector 180 may be disabled or blanked until the next atrial event that causes a new post-atrial time interval to be initiated. In this manner, oversensing event detector 180 may generate an event time signal, such as event time signal 164, only during post-atrial time interval 162. In response to atrial event 152 being a sensed P-wave, e.g., in response to a P-wave sensed event signal 183 (fig. 5) received from atrial channel 87 (or control circuitry 80), post-atrial time interval 162 may be set to a first duration, e.g., 80 ms. When atrial event 152 is an atrial pacing pulse, the post-atrial time interval 162 may be set to a second duration, e.g., 110ms, that is longer than the first duration. Atrial event signals 154 present in ventricular signal 153 may occur relatively later after an atrial pacing pulse than after a sensed P-wave due to a delay between the delivered pacing pulse and the electrical depolarization of the atrial myocardial tissue.

When ventricular signal 153 crosses R-wave sensing threshold 157 during post-atrial time interval 162, oversensing event detector 180 generates event time signal 164 that is used by control circuitry 80 to accumulate the oversensing evidence, e.g., as a count of the event time signal generated by oversensing event detector 180. The control circuit 80 may ignore the event time signal 164 to control ventricular pacing or to determine ventricular rate or rhythm. For example, the control circuit 80 may accumulate oversensing evidence by incrementing the value of the oversensing event counter each time the event time signal 164 is received from the oversensing event detector 180. The control circuit 80 may use the accumulated oversensing evidence, e.g., the value of the oversensing event counter, to determine whether the oversensing criteria are met based on the number of event time signals generated by the oversensing event detector 180 (within the post-atrial time interval) over a predetermined number of ventricular cycles. When oversensing criteria are met, if the post-atrial ventricular blanking period 160 is disabled, given the currently programmed ventricular sensitivity setting and any other sensing threshold control parameters used to control the R-wave sensing threshold 157, then oversensing by the ventricular event detector 176 is likely.

The control circuit 80 uses the event time signal 164 to control ventricular sensing control parameters applied to the ventricular event detector 176, such as to enable or disable the post-atrial ventricular blanking period 160, set an end time 165 of the post-atrial ventricular blanking period 160 (e.g., based on the timing of the event time signal 164 after the atrial event 152), and/or adjust a ventricular sensitivity setting used to control the R-wave sensing threshold 157. The R-wave sensing threshold 157 shown in fig. 6 may be equal to the ventricular sensitivity setting, which is the sensing floor or lowest voltage amplitude that adjusts the auto-adjusting R-wave sensing threshold. The R-wave sensing threshold 157 may be set to a starting value after a ventricular pacing pulse or sensed R-wave and lowered to a ventricular sensitivity setting according to one or more decay rates or step drops, for example to 0.075, 0.1, 0.3.0.45, 0.6, 0.9, or 1.2 millivolts or other programmed values. As described below, the control circuit 80 may be configured to adjust the ventricular sensitivity setting, the end time 165 of the post-atrial ventricular blanking period 160, and/or enable or disable the post-atrial ventricular blanking period 160 based on the oversensing evidence accumulated in response to receiving an event signal (such as the event time signal 164) from the oversensing event detector 180. In addition to the event time signal 164 indicating the time at which the R-wave sensing threshold is off during the post-atrial time interval 162, the oversensing event detector 180 may include a peak detector for determining the maximum peak amplitude 155 and the time of the peak amplitude 155 for events 154 that are off-limit the R-wave sensing threshold 157. The oversensing event detector 180 may generate an amplitude signal (signal 188, fig. 5) that indicates the maximum peak amplitude 155 and/or a peak time signal (signal 187, fig. 5). As described below, the control circuit 80 may use the maximum peak amplitude 155 to determine whether to adjust the ventricular sensitivity setting and/or enable the post-atrial ventricular blanking period 160 to reduce the likelihood of oversensing of the ventricular channel 89, among other accumulated evidence of oversensing. In some instances, the time of the maximum peak may be used to set the end time of the post-atrial ventricular blanking period 160.

In some instances, cardiac potential signal 159 may be present in ventricular signal 153. The cardiac potential signal 159 may be an escherichia beam potential signal or an H-wave and may occur 30ms to 70ms after an atrial event 152 and 20ms to 50ms before the true R-wave. The potential signal 159 may occur during the post-atrial time interval 162, causing the oversensing event detector 180 to generate an event time signal 169 that indicates a time that the R-wave sensing threshold of the oversensing signal may potentially be out-of-limit if the post-atrial ventricular blanking period 160 is disabled or shortened. When the ventricular blanking period 160 is enabled and expires later than the time of the cardiac potential signal 159, the ventricular event detector 176 does not generate the R-wave sensed event signal 163 (as indicated by the dashed line).

The oversensing event detector 180 may generate an amplitude signal indicative of the maximum peak amplitude 161 of the potential signal 159. As described above, the oversensing event detector 180 may additionally or alternatively generate a peak time signal indicative of the time of the maximum peak 161 of the potential signal 159. The control circuit 80 may accumulate oversensing evidence in response to receiving the event time signal 169 (and/or peak amplitude and/or peak time signal) and use the accumulated oversensing evidence and/or event amplitude information to adjust ventricular sensing control parameters, for example, by increasing the ventricular sensitivity setting to be greater than the amplitude of the potential signal 159 and/or enabling or extending the atrial ventricular blanking period 160 so that it expires later in time than the potential signal 159 after the atrial event 152. The control circuit 80 may adjust the duration or end time of the post-atrial time interval 162 based on the timing of the most recent event time signal 159 that occurred during the post-atrial time interval 162. In various instances, the oversensing event time may be determined from the atrial event signal to the most recent event time signal during the post-atrial time interval 162 for each of the plurality of cardiac cycles. The end time of the post-atrial ventricular blanking period 160 and/or the post-atrial time interval 162 may be adjusted based on a measure of the oversensing event time, e.g., based on an average, median, nth longest, or other measure of the timing of the most recent event time signal over one or more cardiac cycles.

While early signal 154, which may correspond to atrial event 152 and potential signal 159, is shown in ventricular signal 153, it should be recognized that in various instances one, both, or neither of

signals

154 and 159 may be present in ventricular signal 153 for a given cardiac cycle. When two or more signals exceed the R-wave sensing threshold 157 during the post-atrial time interval 162, the control circuitry 80 may accumulate oversensing evidence, e.g., as a count of event time signals, in response to one signal or all event time signals generated by the oversensing event detector 180 during a given cardiac cycle. In the example of fig. 6, the control circuit 80 may accumulate oversensing evidence, for example, by incrementing an oversensing event counter by one in response to only one

event time signal

164 or 169, or incrementing oversensing evidence by two in response to each

event time signal

164 and 169.

Late event 156 of ventricular signal 153 crosses R-wave sensing threshold 157. The R-wave sensing threshold 157 may be equal to the ventricular sensitivity setting at this point in the ventricular cycle because the

earlier events

154 and 159 were not sensed by ventricular event detector 176 and are not used to reset the R-wave sensing threshold amplitude to the starting value based on the sensed event amplitude. Late events 156 occur outside of the post-atrial ventricular blanking period 160 and after a post-atrial time interval 162. Ventricular event detector 176 generates an R-wave sensed event signal 168 that is used by control circuitry 80 to control ventricular pacing, e.g., inhibit scheduled ventricular pacing pulses and/or initiate lower rate ventricular pacing intervals. Oversensing event detector 180 may or may not receive ventricular signals 153 outside of post-atrial interval 162. Thus, oversensing event detector 180 does not generate an event time signal in response to event 156 crossing R-wave sensing threshold 157.

In some examples, control circuitry 80 may determine peak amplitude 158 of late events (such as event 156) of event signal 168 that cause ventricular event detector 176 to generate an R-wave sense. The control circuit 80 may use the peak amplitude 158 to determine an R-wave amplitude metric. As described below, when the oversensing evidence criteria are met, the R-wave amplitude metric may be used to determine whether to adjust the ventricular sensitivity settings. In other examples, ventricular event detector 176 may include a peak detector circuit and be configured to detect peak amplitude 158 of late events 156 associated with R-wave sense event signal 168. Ventricular event detector 176 can generate a peak amplitude signal that indicates the magnitude (e.g., in volts or millivolts) of late event 156 that is communicated to control circuit 80. In still other examples, the peak detectors implemented in the oversensing event detector 180 may be enabled to determine the peak amplitudes of both early and late events within and outside the post-atrial time interval 162, such that the oversensing event detector 180 may communicate a peak amplitude signal to the control circuit 80 indicating the peak amplitude 158 of the late event 156.

It should be appreciated that while fig. 4 and 5 depict one example configuration of circuitry for detecting R-wave sensing threshold violations and generating associated time and amplitude signals for accumulating evidence of oversensing and adjusting ventricular sensing control parameters, the functionality disclosed herein may be implemented in various configurations, with one or more circuits and/or processors configured to cooperatively perform the functionality described herein and attributed to IMD 14 or pacemaker 100.

When the post-atrial ventricular blanking 160 is disabled, an R-wave sensing threshold crossing during (or after) the post-atrial time interval 162 may cause the ventricular event detector 176 to generate an R-wave sensed event signal (e.g., 163, 166, or 168). The control circuit 80 maintains the scheduled ventricular pacing pulses in response to receiving the R-wave sensed event signal. The ventricular pacing pulses may be scheduled upon expiration of the AV pacing interval or the VV pacing interval. When post-atrial ventricular blanking is enabled, an R-wave sensing threshold violation (e.g., event 156) outside only the post-atrial ventricular blanking period 160 may cause the control circuit 80 to maintain the scheduled ventricular pacing pulses. The R-wave sensing threshold violation may or may not occur within the post-atrial time interval 162. For example, when post-atrial time interval 162 is longer than post-atrial blanking period 160, ventricular event detector 176 may generate an R-wave sensed event signal in response to an R-wave sensing threshold violation of ventricular signal 153 during post-atrial time interval 162 and non-overlapping portion 167 of post-atrial blanking period 160. The R-wave sensed event signal may cause the control circuit 80 to maintain a scheduled ventricular pacing pulse. Oversensing event detector 180 may generate an event time signal in response to an R-wave sensing threshold violation of ventricular signal 153 during post-atrial time interval 162 and non-overlapping portion 167 of post-atrial blanking period 160. The event time signal during non-overlapping portion 167 causes control circuit 80 to accumulate evidence of oversensing. Thus, during the post-atrial time interval 162, but an R-wave sensing threshold crossing outside of the post-atrial ventricular blanking period may result in maintaining scheduled ventricular pacing pulses and detecting oversensing evidence by the control circuitry 80. The control circuit 80 may extend the post-atrial ventricular blanking period 160 using the oversensing sensed evidence accumulated during the non-overlapping portion 167 to expire later than the event time signal received during the non-overlapping portion 167 and/or to increase the ventricular sensitivity setting to avoid sensing events during the non-overlapping portion 167.

Fig. 7 is a flowchart 200 of a method that may be performed by a medical device (such as IMD 14 or pacemaker 100) for accumulating evidence of oversensing and adjusting ventricular sensing control parameters, according to one example. At block 202, the control circuitry 80 may determine that an R-wave sensing threshold violation has occurred. This determination may be made based on the event time signal 186 received from the oversensing event detector 180 and/or the R-wave sensed event signal 178 received from the ventricular event detector 176. In some examples, R-wave sensing threshold violations occurring during the post-atrial time interval are identified at block 202 for detecting oversensing evidence. For purposes of detecting evidence of oversensing according to the method of fig. 7, R-wave sensing thresholds outside the post-atrial time interval occurring at block 202 may be ignored.

At block 204, the control circuit 80 may determine a time interval from a previous atrial event to the time (or peak amplitude time) at which the R-wave sensing threshold violation occurred and determine whether the determined time interval is less than the oversensing event time interval threshold. The oversensing event time interval threshold may correspond to a post-atrial time interval, such as post-atrial time interval 162 in fig. 6, during which an R-wave sensing threshold violation may be caused by an atrial event (sensing or pacing) or a cardiac potential signal. If the R-wave sensing threshold violation occurs later in the oversensing event time interval threshold, e.g., outside the post-atrial time interval 162, the control circuitry 80 returns to block 202 to wait for the next R-wave sensing threshold violation. An R-wave sensing threshold violation that is later than the oversensing event time interval threshold of the previous P-wave sensed event signal or delivered atrial pacing pulse is not counted as evidence of possible oversensing.

In some examples, the control circuitry 80 may determine that the time from an atrial event (sensing or pacing) to the R-wave sensing threshold crossing is less than the oversensing event time interval threshold based on receiving the event time signal 186 (shown in fig. 5) from the oversensing event detector 180. The oversensing event detector 180 may be enabled to generate the event time signal 186 only during the post-atrial time interval. Thus, when the control circuit 80 receives an event time signal from the oversensing event detector 180, the corresponding R-wave sensing threshold violation is within the oversensing event time interval threshold at block 206. In some cases, control circuit 80 may also receive R-wave sensed event signals from ventricular event detector 176 during the post-atrial time interval when post-atrial ventricular blanking is not enabled or when the post-atrial time interval is longer than the post-atrial ventricular blanking period. However, the event time signal 186 from the oversensing event detector 180 is evidence of whether R-wave sensed event signals may be or are actually oversensing. If an event time signal is not received from the oversensing event detector 180, but an R-wave sensed event signal is received from the ventricular event detector 176 at block 202, the control circuit 80 may determine that the R-wave sensing threshold violation is later than the oversensing event time interval threshold and return to block 202.

In some examples, the oversensing event time interval threshold applied at block 206 may be different when the previous atrial event is a sensed P-wave than when the current atrial event is an atrial pacing pulse. When the previous atrial event that initiated the oversensing event time interval threshold is a pacing pulse, a longer oversensing event time interval threshold may be applied because there is a delay between the delivered atrial pacing pulse and the induced atrial depolarization. For example, when the previous atrial event is a sensed P-wave, the oversensing event time interval threshold or post-atrial time interval may be set to 70ms to 100ms or about 80 ms. When the prior atrial event is an atrial pacing pulse, the time interval threshold or post-atrial time interval may be set to 100ms to 120ms or about 110 ms.

In response to determining that the time from the atrial event to the detected R-wave sensing threshold crossing is less than the oversensing event time interval threshold, the control circuitry 80 detects oversensing evidence at block 208. The detected oversensing evidence may or may not correspond to an actual oversensing event that caused ventricular event detector 176 to generate an erroneous R-wave sensed event signal. When post-ventricular blanking and enablement and R-wave sensing threshold crossing occurs during the post-atrial ventricular blanking period, the oversensing evidence detected at block 208 is evidence of a possible oversensing event, but oversensing does not actually occur or interfere with ventricular pacing control. The oversensing evidence indicates that oversensing may occur or is predicted to occur if post-ventricular blanking is disabled.

At

blocks

212 and 214, the control circuit 80 may determine whether the accumulated oversensing evidence meets the oversensing criteria. In one example, the control circuitry 80 may determine whether oversensing evidence of a cardiac electrical signal violation (e.g., an R-wave sensing threshold) is detected during the post-atrial time interval for a threshold number of consecutive ventricular cycles (or following a threshold number of consecutive atrial sensing and/or atrial pacing events). For example, the control circuitry 80 may determine whether oversensing evidence is detected within the post-atrial time interval for at least three, at least five, or other selected number of consecutive detected R-wave sensing threshold violations. When infrequent or intermittent oversensing evidence is detected based on an isolated R-wave sensing threshold crossing during one post-atrial time interval, the accumulated oversensing evidence may be deemed insufficient to respond by adjusting the ventricular sensing control parameters. Infrequently oversensing atrial events or cardiac potential signals may not interfere with pacing control in a clinically significant manner, such that adjustments to ventricular sensing control parameters that may reduce true R-wave sensing reliability may be considered inappropriate. In some cases, intermittent or infrequent oversensing evidence detection may be associated with intermittent or non-persistent non-cardiac noise or other signal artifacts, which may not require ventricular sensing control parameter adjustments.

The control circuit 80 may detect Z consecutive cycles of oversensing evidence when the oversensing evidence counter is incremented in response to the R-wave sensing threshold crossing during the post-atrial time interval following the Z consecutive atrial events. When post-atrial ventricular blanking is enabled, the threshold number Z of consecutive cycles of detected oversensing evidence may be different than when post-atrial ventricular blanking is disabled. When post-ventricular blanking is enabled, evidence of oversensing may be less likely to cause ventricular pacing pauses. Thus, a higher amount of continuously detected oversensing evidence may be required before performing any additional analysis or taking any additional corrective action. However, when postatrial ventricular blanking is disabled, oversensing of atrial events may result in suspension of ventricular pacing. Thus, the number of consecutive cycles in which evidence of oversensing is detected may be relatively low, e.g., two consecutive cycles, in order to allow the control circuit 80 to take more immediate corrective action by adjusting one or more ventricular sense control parameters.

When oversensing evidence is detected for at least Z consecutive ventricular cycles at block 212, for example, during at least Z consecutive post-atrial time intervals, the control circuit 80 may apply additional oversensing evidence criteria at block 214. For example, the control circuit 80 may additionally require oversensing evidence for Y detected at least X recent cardiac cycles. To illustrate, the control circuit 80 may determine that the oversensing criteria are met at block 214 in response to determining that at least six of the twelve R-wave sensing threshold violations are detected as oversensing evidence and that at least three are detected in succession. As noted above, these thresholds for X and at least Z consecutive oversensing evidence detections of Y cardiac phases in oversensing evidence detection may be defined differently for when postatrial ventricular blanking is enabled than when postatrial ventricular blanking is disabled. The oversensing criteria that should be applied at block 214 do not necessarily need to produce actual false R-wave sensed event signals when oversensing evidence is detected. As described above, oversensing criteria may be detected and accumulated at block 208, e.g., as counts of R-wave sensing threshold crossings over the post-atrial time interval, even when the ventricular event detector 176 applies a post-atrial ventricular blanking period to the ventricular signal, the oversensing criteria may be detected, thereby precluding oversensing of event signals that may occur during the blanking period.

When the oversensing criteria are met at block 214, the control circuit 80 may enable post-atrial ventricular blanking at block 216. In some cases, post-atrial ventricular blanking may already be enabled and, if so, remains enabled. In other cases, post-atrial ventricular blanking may not be currently enabled, and the accumulated oversensing evidence ensures that post-atrial ventricular blanking can be enabled regardless of whether actual oversensing occurred to avoid or minimize the possibility of oversensing by ventricular event detector 176.

The post-atrial ventricular blanking period may be set to a fixed value or may be adjusted based on determining the time from a P-wave sensed event signal or an atrial pacing pulse to an R-wave sensing threshold identified as evidence of oversensing. For example, a default maximum post-atrial ventricular blanking period may be enabled, however, if the time interval from the previous atrial event to the R-wave sensing threshold identified as oversensing evidence is a safe interval that exceeds less than the default maximum post-ventricular blanking period, the blanking period may be shortened. The blanking period may be shortened by a predetermined decrement. For example, the 120ms maximum blanking period may be shortened to 110ms or 100ms as long as the post-atrial ventricular blanking period is at least longer than the oversensing evidence event time signal following the atrial event, e.g., later than the oversensing event time signal following the atrial event. In other examples, the post-atrial ventricular blanking period may be reduced from a maximum period to an interval that is a predetermined safety interval (e.g., 10 to 30ms) or a predetermined percentage longer than the time interval from the most recent previous atrial event to the event detected as evidence of oversensing. This time interval may be determined by the control circuit 80 at block 204, for example, in response to an event time signal received from the oversensing event detector 180 (fig. 5).

In other examples, control circuitry 80 may determine a plurality of a-OS (atrial-to-oversensing event) time intervals between many-to-one atrial event and one subsequent R-wave sensing threshold identified as evidence of oversensing. The longer a-OS time interval may be determined when, for example, two events associated with atrial events and two events associated with cardiac potential signals occur during a post-atrial time interval. The control circuit 80 may determine the maximum a-OS time interval at block 216 in response to the oversensing criteria being met. The maximum a-OS time interval may be determined from the detected oversensing evidence that contributes to the satisfaction of the oversensing criteria at block 214. The control circuit 80 may set a post-atrial ventricular blanking period at block 216 based on the maximum a-OS time interval. For example, the post-atrial ventricular blanking period may be set equal to or at a predetermined safety interval or a predetermined percentage longer than the maximum A-OS interval. Thus, the post-atrial ventricular blanking period may be a variable time period and may be limited up to some maximum allowed blanking period, for example up to a maximum of 120 or 130 ms.

When the post-atrial ventricular blanking is enabled at block 216, two different blanking periods may be applied by ventricular event detector 176. A shorter blanking period may be initiated in response to receiving a P-wave sensed event signal and a longer blanking period may be initiated in response to delivery of an atrial pacing pulse. For example, the post-atrial ventricular blanking period set in response to a P-wave sensed event signal may be 80ms and the blanking period set in response to an atrial pacing pulse may be 110ms, although shorter or longer blanking periods may be selected and may be tailored to a given patient. As described above, each of the post-atrial sensed event ventricular blanking period and the post-atrial paced event ventricular blanking period may be based on an a-OS time interval setting determined after an atrial sensed P-wave and after an atrial pacing pulse, respectively.

When the oversensing criteria are not met at block 214, the control circuit 80 may disable the post-atrial ventricular blanking at block 218. If ventricular post-ventricular blanking is enabled and applied by the ventricular event detector 176, but the accumulated oversensing evidence fails to meet the oversensing criteria at block 214, the post-atrial ventricular blanking may be disabled at block 218, with a reasonably low risk of a false R-wave sensed event signal being generated by the ventricular event detector 176. When oversensing is determined to be unlikely, disabling post-atrial ventricular blanking can enable R-wave sensing during a greater portion of the ventricular cycle to improve R-wave sensing reliability for pacing control and rhythm detection based on oversensing criteria not met at block 214. For example, being able to sense R-waves during a greater portion of the ventricular cycle may improve detection of fast ventricular rhythms such as ventricular tachycardia or fibrillation. In some cases, the post-atrial ventricular blanking may have been disabled when it is determined that the oversensing criteria are not met at block 214, in which case the post-atrial ventricular blanking remains disabled at block 218.

After enabling or disabling the post-atrial ventricular blanking at one of

blocks

216 or 218, the control circuit 80 returns to block 202 to wait for the next R-wave sensing threshold violation. The process of flowchart 200 may be performed periodically or continuously in response to each R-wave sensing threshold crossing. The atrial post-ventricular blanking is enabled or remains enabled each time the oversensing criteria are met. The post-atrial ventricular blanking is disabled or remains disabled each time the oversensing criteria are not met. The frequency of enabling and disabling post-atrial ventricular blanking is limited by setting the oversensing criteria used at block 214. For example, Z consecutive R-wave sensing threshold violations need to be identified as oversensing evidence and X of Y R-wave sensing threshold violations need to be identified as oversensing evidence before the oversensing criteria can be met, preventing frequent disabling and re-enabling of post-atrial ventricular blanking, and requiring enough of the possible oversensing evidence to enable blanking. In this way, post-atrial ventricular blanking is not possible to repeatedly and frequently enable and disable, e.g., on alternating heartbeats. The Z consecutive R-wave sensing threshold violations identified as evidence of oversensing may need to be R-wave sensing threshold violations occurring during Z consecutive post-atrial time intervals, e.g., based on the event time signals generated by the oversensing event detector 180, if an R-wave sensing threshold violation occurs outside of the post-atrial time interval with or without interference and is associated with an R-wave sensed event signal.

Fig. 8 is a flow chart 300 of a method for accumulating evidence of oversensing and adjusting a ventricular sensing control parameter based on the accumulated evidence, according to another example. At block 302, the control circuit 80 identifies an R-wave sensing threshold violation as described above in connection with fig. 7. The R-wave sensing threshold violation may be identified in response to an event time signal from the oversensing event detector 180. The time from the most recent previous atrial event (sensed or paced) to the R-wave sensing threshold crossing may be determined at block 304.

At block 305, the control circuit 80 may determine a maximum peak amplitude of the ventricular signal after the R-wave sensing threshold is exceeded. As described above in connection with fig. 5, the peak amplitude may be determined by the oversensing event detector 180 and the amplitude signal 188 may be passed to the control circuit 80. In other examples, the control circuit 80 may receive a ventricular EGM signal 185 from the ventricular channel 89 and an event time signal 186 from the oversensing event detector 180. The control circuit 80 may determine the maximum peak amplitude of the ventricular EGM signal 185 after the event time signal 186 but within the post-atrial time interval. The peak time signal 187 may be communicated to the control circuit 80 for marking the peak time of the event. In various examples disclosed herein, the control circuit 80 may use the time at which the R-wave sensing threshold is out-of-limit or the time of the peak amplitude as the event time, e.g., for determining a time interval from an atrial event at block 304. At other times, the control circuit 80 may identify an R-wave sensing threshold violation at block 302 based on the R-wave sensed event signal 178 received from the ventricular event detector 176 and determine a maximum peak amplitude of the ventricular EGM signal 185 following the R-wave sensed event signal.

If the determined time interval from the previous atrial event to the identified R-wave sensing threshold violation (or peak time) is not less than the oversensing event time interval threshold ("none" branch of block 306), e.g., within the post-atrial time interval, then no evidence of oversensing is detected. The peak amplitude determined at block 305 may be used to update a measure of the R-wave amplitude at block 310. For example, the peak amplitudes determined at block 305 that are not detected as evidence of oversensing may be used to determine a running average, median, minimum, or other measure of sensed R-wave amplitude. The R-wave amplitude metric may be determined based on the most recent 3, 6, 8, 12, 20, or other predetermined number of R-wave sensing threshold violations that were not detected as oversensing evidence. After updating the R-wave amplitude metric at block 310, the control circuit 80 returns to block 302 to wait for the next R-wave sensing threshold violation.

When oversensing evidence is detected at block 308, for example based on the time at which the R-wave sensing threshold from the most recent previous atrial event within the post-atrial time interval is out-of-limit (or peak time), the control circuitry 80 may determine an oversensing event amplitude metric at block 311. The maximum peak amplitude after the R-wave sensing threshold violation determined at block 305 may be used to update the oversensing event amplitude metric at block 311. The oversensing event amplitude metric may be updated to equal an average, median, maximum, or other metric determined from a predetermined number of R-wave sensing threshold violations most recently detected as evidence of oversensing. For example, the highest maximum peak amplitude value of the last 3 to 12 peak amplitudes determined for an event identified as oversensing evidence may be updated as the oversensing event amplitude metric at block 311. It should be noted that the oversensing event amplitude metric may be determined from the signals identified as evidence of oversensing, which may or may not actually be oversensed as false R-waves or event signals that cause R-wave sensing are generated by ventricular event detector 176.

At block 312, the control circuit 80 determines whether at least Z consecutive R-wave sensing threshold violations are detected as oversensing evidence. If not, the control circuit 80 may update the oversensing evidence counter to track the oversensing evidence at block 312 and return to block 302. For example, the continuous Z oversensing evidence counter may be reset to zero. The Y value of the X/Y counter may be incremented. If oversensing evidence is detected for the Z consecutive R-wave sensing threshold violations determined at block 312, the control circuit 80 determines whether oversensing criteria are met at block 314. As described above, it may be desirable for X out of Y consecutive R-wave sensing threshold violations to be detected as oversensing evidence. If not, the control circuit 80 may disable the post-atrial ventricular blanking (or the blanking may remain disabled) at block 318 and return to block 302.

When the oversensing criteria are met at block 314, the control circuit 80 may analyze the oversensing event amplitude metric and/or the R-wave amplitude metric at block 320. Based on this analysis, the control circuit 80 may select an adjustment to the ventricular sense control parameter. For example, the control circuit 80 may select between enabling post-atrial ventricular blanking and adjusting ventricular sensitivity to reduce the likelihood of oversensing by the ventricular event detector 176. To choose to adjust ventricular sensitivity rather than enable post-atrial ventricular blanking in response to satisfying the oversensing criteria, it may be desirable for the R-wave amplitude metric to be greater than the oversensing event amplitude metric and/or greater than the current ventricular sensitivity setting by at least some factor.

For example, at block 320, the R-wave amplitude metric may be compared to the oversensing event amplitude metric. The R-wave amplitude metric may require a predetermined multiple, percentage, or fixed difference greater than the oversensing event amplitude metric in order to select a ventricular sensitivity adjustment rather than enabling post-atrial ventricular blanking. For example, it may be desirable for the R-wave amplitude metric to be at least two times or at least three times the oversensing event amplitude metric.

Additionally or alternatively, at block 322, the R-wave amplitude metric may be compared to a current ventricular sensitivity setting used to control the R-wave sensing threshold. The R-wave amplitude metric may require at least a predetermined multiple, percentage, or fixed difference greater than the sensitivity setting, e.g., two or three times greater than the current ventricular sensitivity setting, in order to select a ventricular sensitivity adjustment rather than enabling post-atrial ventricular blanking.

When the R-wave amplitude metric does meet the amplitude criteria relative to the oversensing amplitude metric and/or relative to the current ventricular sensitivity setting, the control circuit 80 may choose to adjust ventricular sensitivity at block 324. In various instances, it may be desirable to meet one or both of the requirements represented by

blocks

320 and 322 in order to select a ventricular sensitivity adjustment at block 324. Ventricular sensitivity may be adjusted by predetermined increments, such as 0.1 millivolts, 0.2 millivolts, 0.25 millivolts, 0.3 millivolts, 0.5 millivolts, or other increments. In other examples, the ventricular sensitivity setting may be adjusted to a setting greater than the oversensing event amplitude metric by a predetermined magnitude difference, multiple, or percentage of the oversensing event amplitude metric. The ventricular sensitivity setting may be increased to a maximum that is a fraction or percentage of the R-wave amplitude metric, such as one-half or one-third of the R-wave amplitude metric.

When the R-wave amplitude metric is not sufficiently greater than the oversensing event amplitude metric and/or the ventricular sensitivity setting ("no" branch of blocks 320 and/or 322), or the ventricular sensitivity setting cannot be adjusted to a value sufficiently greater than the oversensing event amplitude metric and less than the R-wave amplitude metric, the control circuit 80 may choose to enable post-atrial ventricular blanking instead of adjusting the ventricular sensitivity setting. The control circuit 80 may enable post-atrial ventricular blanking at block 316.

In some instances, a clinician or user may be able to program a medical device to automatically enable and disable post-atrial ventricular blanking. However, the clinician or user may choose to "turn off" the automatic enabling and disabling of the post-atrial ventricular blanking period for some patients. For example, if posterior ventricular blanking is enabled, a patient with a history of tachyarrhythmias may be at risk for ventricular tachyarrhythmias. Thus, the user may select the auto-enable and disable feature that turns off the post-atrial ventricular blanking of some patients.

When the automatic adjustment to blanking is programmed to "on," as determined at block 326, the control circuit 80 may automatically enable and disable the post-atrial ventricular blanking in response to the oversensing criteria being met or not being met, respectively. When the clinician or other user programs the automatic adjustment of the post-atrial ventricular blanking to be off, the post-atrial ventricular blanking is permanently disabled and cannot be automatically enabled by the control circuit 80 until the user programs the post-atrial ventricular blanking adjustment to be on.

If the automatic blanking period adjustment is programmed to be on when the oversensing criteria are met but the R-wave amplitude metric fails to meet the ventricular sensitivity adjustment criteria ("yes" branch of block 326), the control circuit 80 can enable post-atrial ventricular blanking at block 316. The post-atrial ventricular blanking period may be set to a predetermined maximum blanking period or a maximum a-OS time interval determined based on the R-wave sensing threshold from an atrial event to detection as evidence of oversensing. As described above, the control circuit 80 may set the post-atrial ventricular blanking period after the atrial sensed event to a shorter time interval than the post-atrial ventricular blanking period after the atrial pacing pulse. Each of these post-atrial sensing and post-atrial pacing ventricular blanking periods may be based on a time interval measured from the respective atrial sensing and atrial pacing event to the respective R-wave sensing threshold violation detected as evidence of oversensing.

When the automatic adjustment of post-atrial ventricular blanking is programmed to be off (the "no" branch of block 326), the control circuit 80 may maintain the adjustment of the ventricular sensing control parameters in response to the oversensing criteria being met and the R-wave amplitude metric not meeting the criteria required to adjust ventricular sensitivity. In this case, the control circuit 80 may provide one or more other responses to the satisfaction of the oversensing criteria. In some instances, the control circuitry 80 may generate a notification or report of the oversensing evidence at block 328, e.g., transmitted to an external device such as the device 50 in fig. 1. The notification or report may be stored in memory 82 until the next interrogation session with external device 50. In other instances, a notification or report may be transmitted to the external device 50 without delay to alert the patient or clinician that oversensing may occur and may interfere with proper therapy delivery.

The patient or clinician may receive notifications or reports from the external device 50. The patient may, for example, receive an oversensing notification and be instructed to seek medical advice or attention so that his/her clinician can view the oversensing evidence and reprogram ventricular sensing control parameters or other IMD control parameters as needed. In other examples, a clinician may receive an oversensing evidence report via external device 50 through a remote patient monitoring system and send programming instructions to external device 50 to reprogram IMD control parameters, which may include ventricular sensing control parameters, or at least enable automatic post-atrial ventricular blanking adjustments.

Additionally or alternatively, the control circuit 80 may adjust the ventricular sensing control parameters by enabling post-atrial safety pacing at block 330 when the oversensing criteria are met and the post-atrial blanking period is automatically enabled to be "off. In some instances, automatic enablement of post-atrial safety pacing may be a programmable feature. For example, the clinician may be able to automatically enable and disable the programming of post-atrial safety pacing by turning the control circuit 80 on or off. When post-atrial safe pacing is enabled, the control circuit 80 may enable a post-atrial safe pacing interval at block 330. The post-atrial safe pacing interval is the sensing window during which any R-wave sensed event signals generated by ventricular event detector 176 are largely oversensed atrial events or oversensed cardiac potential signals. Therapy delivery circuitry 84 may be configured to generate a ventricular safe pacing pulse in response to an R-wave sensed event signal received within a post-atrial safe pacing interval following an atrial sensed or paced event. The ventricular safe pacing pulses may be generated and delivered at the expiration of a post-atrial safe pacing interval. The post-atrial safe pacing interval may be a time interval at least encompassing the ventricular physiologic refractory period, such that if the R-wave sensing threshold violation during the atrial safe pacing interval is a true R-wave, the ventricular safe pacing will fail to capture the ventricle due to the His-Purkinje system and/or refractoriness of the ventricular myocardial tissue. If an R-wave sensing threshold violation during a post-atrial safety pacing interval is an atrial event that is erroneously sensed as an R-wave, then ventricular safety pacing may capture and produce a ventricular beat because the cardiac tissue is not in a refractory state.

A post-atrial safety pacing interval may be set after the atrial sensed event (P-wave sensed event signal) and the atrial pacing pulse. After an atrial event (sensing or pacing), control circuitry 80 may initiate a safe pacing interval, which may be set in some instances to a shorter interval after the atrial sensed event following the atrial pacing pulse. In some examples, the safe pacing interval may be equal to a post-atrial time interval or a post-atrial ventricular blanking period. In addition, the control circuit 80 may initiate an AV pacing interval (for delivering ventricular pacing pulses synchronized with the atrium) in response to the atrial event. Therapy delivery circuitry 84 generates and delivers ventricular pacing pulses at the expiration of the safe pacing interval in response to R-wave sensed event signals produced by ventricular event detector 176 during the safe pacing interval. Therapy delivery circuitry 84 maintains the safe pacing when the R-wave sensed event signal is not generated during the safe pacing interval and delivers the scheduled ventricular pacing pulse at the expiration of the AV pacing interval. When an R-wave sensed event signal is generated by ventricular event detector 176 after the safe pacing interval but before the expiration of the AV pacing interval, the ventricular pacing pulse scheduled at the AV pacing interval may be maintained. During single chamber ventricular pacing, ventricular pacing pulses may be scheduled at a lower rate VV pacing interval instead of the AV pacing interval, and delivered at the expiration of the lower rate VV pacing interval in the absence of R-wave sensed event signals during the safe pacing interval and the VV pacing interval.

Since the control circuit 80 is configured to suppress ventricular pacing pulses scheduled at AV intervals or VV intervals in response to R-wave sensed event signals, enabling a safe pacing interval after an atrial event avoids a pause in ventricular rhythm when the R-wave sensed event signals are false. Adjusting the ventricular sensing control parameters by setting the safe pacing interval allows the control circuit 80 to identify possible oversensing events when post-atrial ventricular blanking is disabled and avoid ventricular rhythm pauses due to oversensing.

Although not explicitly shown in fig. 8, the post-ventricular safe pacing, if enabled, may be disabled at 316 when the post-atrial ventricular blanking is disabled. In response to receiving the oversensing evidence notification or report (block 328), the user or clinician may program an automatic adjustment of the post-atrial ventricular blanking. The next time the oversensing criteria are met at block 314 and the R-wave amplitude metric does not meet the criteria required to adjust the ventricular sensitivity setting, the control circuit 80 may enable post-atrial ventricular blanking and disable post-atrial safe pacing at block 316. In some instances, post-atrial safety pacing may be disabled after only atrial sensed events (P-wave sensed event signals), but regardless of whether blanking is enabled, post-atrial safety pacing may remain enabled after atrial pacing events because atrial pacing artifacts may be more likely to be oversensed by ventricular channel 89 than atrial P-waves.

Further, it should be appreciated that any ventricular sense control parameter adjustments made in response to the oversensing criteria being met may be reversed when the oversensing criteria are no longer met. For example, when the oversensing criteria are not met at block 314 and the post-atrial ventricular blanking is disabled at block 318, the post-atrial safety pacing that has been previously enabled at block 330 may be disabled in response to not meeting the oversensing criteria. At block 318, post-atrial safety pacing may be disabled in combination with disabling post-atrial ventricular blanking. Post-atrial safety pacing may be disabled at least after an atrial sensed event. When the post-atrial blanking is disabled at block 318, the post-atrial safety pacing may remain enabled after the atrial pacing pulse, at least in some instances, because oversensing of atrial pacing artifacts may occur when blanking is disabled.

When the ventricular sensitivity setting has been increased at block 324 in response to the oversensing criteria being met and the R-wave amplitude metric meeting the sensitivity adjustment criteria, the ventricular sensitivity setting may be decreased to a lower setting at block 318 in response to the oversensing criteria no longer being met at block 314. In some cases, in addition to disabling the post-atrial ventricular blanking, the ventricular sensitivity setting (in millivolts) may be decreased at block 318. To reduce the ventricular sensitivity setting in conjunction with disabling blanking at block 318, it may be desirable for the R-wave amplitude metric to be greater than the reduced sensitivity setting by a predetermined multiple and/or greater than the oversensing event amplitude metric by a predetermined multiple. In some instances, it may be desirable for the oversensing event amplitude metric to be less than the reduced sensitivity setting by at least a safety margin.

Criteria may be applied to the R-wave amplitude metric and the oversensing event amplitude metric, the R-wave amplitude metric and the relative difference or ratio pending, decreasing the ventricular sensitivity setting, and/or the oversensing event amplitude metric and the pending, and then decreasing the ventricular sensitivity setting before adjusting the ventricular sensitivity setting to the decreased setting. To illustrate, it may be verified that the R-wave amplitude metric is at least two to three times greater than the pending reduced sensitivity setting, and/or that the oversensing event amplitude metric may need to be less than the reduced sensitivity setting. If the criteria for decreasing the sensitivity setting are not satisfied, the sensitivity setting may remain at the previously increased sensitivity setting even if the oversensing criteria are no longer satisfied at block 314.

Fig. 9 is a flow diagram 400 of a method for controlling a ventricular sense control parameter based on oversensing evidence in the presence of atrial Arrhythmia (AT), according to an example. Atrial arrhythmias, which may include different forms of rapid atrial rhythms (such as atrial flutter, atrial tachycardia, and atrial fibrillation) may be detected by the control circuitry 80 at block 401 based on: analysis of the digital EGM signal generated by the sensing circuit 86 and passed to the control circuit 80, and/or analysis of the PP intervals between successive P-wave sensed event signals, RR intervals between successive R-wave sensed event signals, PP intervals between, RP and/or PP intervals between successive P-wave sensed event signals and R-wave sensed event signals. The control circuit 80 may switch from the atrial-tracked ventricular pacing mode to the temporary non-tracking ventricular pacing mode (block 402) in response to detecting the AT to facilitate a regular ventricular rate during the AT that does not track the fast atrial rate. In the absence of R-wave sensed event signals, ventricular pacing pulses may be delivered at a programmed ventricular lower rate interval.

During an AT, the amplitude of the atrial signal may be relatively low compared to a normal sinus P-wave signal, such that atrial event oversensing by ventricular event detector 176 may be less likely to occur during an AT than during a normal sinus or paced rhythm. However, in some cases, atrial event oversensing (or oversensing of cardiac potential signals) may still occur during the AT, and because atrial depolarizations occur AT a fast and sometimes irregular rate depending on the type of AT, atrial events may be oversensing frequently and/or AT irregular intervals by ventricular event detector 176, causing ventricular pacing pulses to be suppressed. If post-ventricular blanking is enabled when an AT is detected, blanking of the true R-wave (which occurs AT an irregular rate) may occur potentially leading to competitive ventricular pacing. In this case, ventricular pacing pulses may be delivered at the expiration of the VV lower rate interval even if intrinsic ventricular depolarization occurs during the post-atrial ventricular blanking. Thus, the techniques for accumulating evidence of oversensing during AT, particularly when enabling posterior ventricular blanking, may be modified from the techniques described in connection with fig. 7 and 8 that may be used during normal sinus or paced heart rhythms.

When the post-atrial blanking is not enabled during the detected AT ("no" branch of block 404), the control circuitry 80 may continue to accumulate evidence of oversensing and adjust ventricular sensing control parameters according to the techniques of fig. 7 or 8. When postatrial ventricular blanking is disabled, the risk of competitive ventricular pacing is low because ventricular event detector 176 is not unaware of the true R-wave occurring early after an atrial event. Thus, special monitoring of oversensing evidence may not be required during AT as long as blanking is disabled. However, if it is detected that post-ventricular blanking is enabled AT time AT, or enabled due to the oversensing criteria being met AT block 406 according to the techniques of fig. 7 or 8, or enabled during a sustained AT, the control circuit 80 may modify the technique for monitoring for evidence of oversensing during AT according to the flowchart of fig. 9. Since atrial event oversensing may occur AT rapid and/or irregular intervals during an AT, atrial event oversensing may occur AT different times in the ventricular cycle, and even multiple times during the ventricular cycle. Detection of oversensing evidence during AT may be more challenging than during slower, sinus or paced rhythms. However, because competitive ventricular pacing may occur when blanking is enabled, the technique of fig. 9 may be performed to detect evidence of oversensing and respond appropriately to minimize the likelihood of competitive ventricular pacing and ventricular rhythm due to oversensing.

If post-ventricular blanking is enabled ("yes" branch of block 404), the control circuit 80 may determine whether the ventricular rhythm is primarily a pacing rhythm at the programmed ventricular rate at block 408. When no (or very little) R-waves are sensed, the absence of R-wave sensed event signals is an indication that the patient is pacemaker dependent. Oversensing is not believed to be possible if no R-wave sensed event signal or several R-wave sensed event signals occur outside the atrial late ventricular blanking period. Thus, as long as the primarily paced ventricular rhythm persists, it is unnecessary to search for sensed events that may be oversensed events. Without evidence of R-wave sensing, the patient is receiving adequate ventricular rate support and the likelihood of competitive ventricular pacing is small.

Based on a predetermined number of consecutive pacing pulses or a very small ratio of R-wave sensed event signals to delivered ventricular pacing pulses, e.g., 1:5, 1:6, 1:8, 1:10, 1:20, or even lower, a primary ventricular pace may be identified at block 408. The threshold for detecting primary ventricular pacing may be modulated based on the pacing history. For example, if the patient has been highly dependent on the pacemaker, e.g., has a high percentage of ventricular pacing, then primary pacing may be true, and therefore a lower primary pacing threshold may be used.

When primary pacing is detected at block 408, the control circuitry 80 may determine whether the primary pacing has lasted for a threshold time interval (or number of pacing cycles). When pacing is detected for at least one minute in one example, sustained primary pacing may be detected. When continuous ventricular pacing is detected, the control circuit 80 may suspend any further monitoring for oversensing evidence AT block 422 as long as an AT is detected. Ventricular rate support is provided correctly and the risk of ventricular competitive pacing is acceptably low. Atrial blanking may be maintained after the ventricles. In some instances, the control circuit 80 may suspend operations for collecting evidence of oversensing during a detected AT episode AT block 422. The control circuit 80 may return to block 401 and repeat the process of flow chart 400 the next time an AT episode is detected. In other examples, the control circuit 80 may temporarily suspend operation for collecting evidence of oversensing for a predetermined time interval, e.g., one minute, two minutes, five minutes, or other time interval, which may be an increased time interval, AT block 422, and then return to block 407 to determine whether AT is still detected in the post-atrial ventricular blanking enable and predominantly continuous ventricular pacing.

If sustained ventricular pacing is not detected, the control circuit 80 may wait at block 410 for the primary ventricular pacing to become sustained (by returning to block 408). However, if the control circuit 80 no longer detects primary ventricular pacing AT block 408 (and still detects an AT episode), the control circuit 80 may perform the modified oversensing monitoring technique that begins AT block 412. At block 412, the control circuit 80 switches to a test mode to monitor for oversensing evidence. The test pattern may be applied for at least one ventricular cycle. For example, when an AT is detected, the control circuit 80 may switch to operate in a temporary non-atrial tracking pacing mode (block 402) and may enable post-atrial ventricular blanking (block 404). In response to not detecting primary ventricular pacing in the temporary non-atrial-tracking ventricular pacing mode, the control circuitry 80 may be configured to switch from the temporary non-atrial-tracking ventricular pacing mode to a test mode of atrial-tracking ventricular pacing at block 412 with post-atrial ventricular blanking disabled. In some instances, the pacing mode is switched to an atrial tracking mode in which post-atrial ventricular blanking is disabled for only a single ventricular cycle, and then returned to a temporary non-atrial tracking ventricular pacing mode in which blanking is re-enabled. In other examples, the control circuit 80 may switch to a test mode of an atrial tracking ventricular pacing mode in which post-atrial ventricular blanking is disabled for up to three or another limited number of ventricular cycles.

At block 414, the control circuit 80 updates an R-wave sensed event counter for each R-wave sensed event signal received from the ventricular event detector 176 during the atrial tracking pacing mode with the post-atrial ventricular blanking disabled. An R-wave sensed event counter may be used to count the number of R-wave sensed event signals occurring within the post-atrial time interval of an atrial event. A second R-wave sensed event counter may be used to count the number of R-wave sensed event signals that occur after the post-atrial time interval. For example, the early sensed event counter may be incremented in response to an event time signal generated by the oversensing event detector 180 interacting with the R-wave sensed event signal 178 generated by the ventricular event detector 176. When the corresponding event time signal 186 is not generated by the oversensing event detector 180 (which may be disabled outside of the post-atrial time interval), a different late sensed event counter may be incremented in response to the R-wave sensed event signal 178 generated by the ventricular event detector 176. Each time the atrial tracking ventricular pacing mode is active, an R-wave sensed event counter is updated according to the timing of the R-wave sensed event signal relative to the post-atrial time interval.

At block 416, based on the counter value updated at block 414, the control circuit 80 determines whether the R-wave sensed events during the test mode occurred only during the post-atrial time interval or if a ventricular pacing pulse (no R-wave sensed event signal) occurred. If only ventricular pacing is occurring during the test pacing mode, then both counter values will be zero. If an R-wave sensed event signal occurs only during the post-atrial time interval, the corresponding early event counter will be non-zero, while the late event counter corresponding to an R-wave sensed event signal outside of the post-atrial time interval will be zero. If only early post-atrial events are sensed and/or ventricular pacing is delivered during the test mode, the control circuit 80 switches back to the temporary non-atrial tracking ventricular pacing mode (from the test pacing mode) to re-enable post-ventricular blanking at block 418. Early events are evidence of potential oversensing, requiring atrial posterior ventricular blanking.

Accordingly, in response to determining that the R-wave sensed event signal generated during the test pacing mode is an early event occurring during the post-atrial time interval, an oversensing evidence counter may be incremented at block 418. At block 420, the oversensing evidence counter may be compared to a threshold. The oversensing threshold may require that evidence of oversensing (or a criterion for the other X of Y) be detected at least six times, for example, in nine test pacing mode cycles. When the oversensing evidence threshold is exceeded, the probability of oversensing during the detected AT is high. AT block 422, the test mode and oversensing evidence monitoring during the AT may be suspended, enabling atrial post-ventricular blanking. The test mode during AT may be suspended when the oversensing evidence counter reaches a threshold of AT least 3, 5, 8, 12, or other predetermined number of test mode ventricular cycles, which may or may not require continuity, determined to be oversensing evidence. Operations for collecting evidence of oversensing during an AT episode, such as switching to a test mode of atrial tracking ventricular pacing with postatrial blanking disabled and updating an R-wave sensed event counter, may pause for the remainder of the currently detected AT episode AT block 422. The control circuit 80 may return to block 401 to wait for the next AT episode detection. In other examples, the control circuit 80 may temporarily suspend the test mode for a predetermined time interval AT block 422 and then return to block 407 to resume accumulating evidence of oversensing according to the modified technique of fig. 9 if an AT is still detected.

When the oversensing evidence counter is not greater than the threshold at block 420, the control circuit 80 may return to block 407. As long as AT is still detected, ventricular blanking is still enabled, and ventricular pacing is not dominant during the temporary non-atrial tracking pacing mode, the control circuit 80 may continue to accumulate evidence of oversensing by briefly switching to the test mode AT block 412. The early R-wave sense event counter and the late R-wave sense event counter may retain their respective current values and continue to increment based on the timing of the R-wave sensed event signals during the test mode. The R-wave sensed event counter may be cleared (reset to zero) when the control circuit 80 suspends switching to test mode AT block 422 or when AT is no longer detected.

If the late event counter corresponding to the R-wave sensed outside of the post-atrial time interval is non-zero and the early sensed event counter corresponding to the R-wave sensed during the post-atrial time interval is zero, control circuitry 80 determines at block 430 that only "late" R-waves have not occurred during the post-atrial time interval. In this case, the control circuit 80 may decrement the oversensing evidence counter at block 432. When blanking is disabled, no R-wave is sensed during the post-atrial time interval, so there is no evidence of possible oversensing.

If the oversensing evidence counter value becomes less than the "no oversensing" threshold at block 434, for example, less than 2 after a predetermined number (e.g., 12) of test mode ventricular cycles, the control circuit 80 may disable the post-atrial ventricular blanking at block 436. Switching to test mode may also be suspended at block 436 because the post-atrial blanking is no longer enabled. Oversensing evidence monitoring may be terminated until an AT event is no longer detected. In some examples, oversensing evidence monitoring may continue during the AT episode (AT block 406) when post-atrial blanking is disabled according to the techniques described in connection with fig. 7 or 8.

When the oversensing evidence counter value is not less than the "oversensing" threshold at block 434, the control circuit 80 continues to intermittently switch to the test mode at block 412 ("no" branch of block 434). The control circuit 80 may switch to the test pacing mode for one ventricular cycle every five cycles, every ten cycles, or other selected frequency to continue to accumulate evidence of oversensing (or lack thereof).

In some cases, there may be a mixture of early and late R-wave sensing events during the test mode. When both the early and late R-wave sense event counters have non-zero values, control circuit 80 proceeds from block 430 (the "no" branch) to block 435. A mix of early and late R-wave sensed events may indicate evidence of oversensing of rapid and/or irregular atrial rates. In response to detecting a combination of early (during the post-atrial time interval) and late (after the post-atrial time interval) R-wave sensing events, an oversensing evidence counter may be incremented at block 435.

The control circuitry 80 may determine at block 439 whether the oversensing evidence meets the oversensing evidence criteria in response to increasing the oversensing evidence at block 435. Oversensing evidence criteria applied to the accumulated oversensing evidence in the process of flowchart 400 or any other flowchart presented herein may include fixed or adjustable thresholds. An adjustable oversensing evidence threshold may be set based on a ratio of the post-atrial time interval to the atrial event interval. The atrial event interval may be a PP interval determined between event signals sensed by successive P-waves generated by the atrial channel of the sensing circuitry 86. In other cases, the atrial event interval may begin and/or end with an atrial pacing pulse. In the case of flowchart 400, AT block 439 the control circuitry 80 may determine an atrial event interval for the detected AT interval from the PP interval. During AT, R-waves may occur randomly during any portion of the AT interval, resulting in a mix of early and late R-wave sensing events ("none" branch of block 430). If the post-atrial time interval is, for example, one-third of the total AT interval, then the true R-wave is expected to occur one-third of the time during the post-atrial time interval and two-thirds of the time after the post-atrial time interval. Accordingly, the control circuitry 80 may set the oversensing evidence threshold AT block 439 as a ratio of the post-atrial time interval to the detected AT interval, e.g., one third in the illustrative example. If more than one-third of the R-wave sensed event signals are early, then at least some of these early R-wave sensed event signals may be evidence of oversensing during the post-atrial time interval. Thus, the ratio of the early event counter value to the late event counter value may be compared to an oversensing evidence threshold AT block 439, which is set (may be variable) based on the ratio of the post-atrial time interval to the AT interval. The oversensing evidence threshold ratio applied AT block 439 may be adjusted when the AT interval changes within or between detected AT episodes.

When this oversensing threshold ratio is not exceeded AT block 439, the control circuit 80 may return to block 412 to repeat the test pacing mode for monitoring additional ventricular cycles oversensing during the detected AT episode. Although not explicitly shown in fig. 9, it should be understood that when an AT event is no longer detected, the control circuit 80 may suspend the test mode and return to block 401 to wait for the next AT episode detection.

When the oversensing evidence threshold ratio (or another fixed oversensing evidence threshold) is exceeded at block 439, the control circuitry 80 may attempt to adjust ventricular sensitivity at block 438 to reduce or eliminate the risk of oversensing. At block 437, the control circuit 80 may determine whether the R-wave amplitude criteria are met. Control circuitry 80 may compare the amplitude metric of the early events sensed during the post-atrial time interval to the amplitude metric of the late events sensed outside of the post-atrial time interval or a previously stored R-wave amplitude metric. As described above in connection with fig. 8, if the R-wave amplitude metric is at least a predetermined multiple, e.g., at least two times, the programmed ventricular sensitivity setting, the control circuit 80 may increase the ventricular sensitivity setting at block 438 to reduce the likelihood of oversensing. In some instances, the R-wave amplitude metric may need to be greater than the oversensing event amplitude metric determined from the early events by a predetermined multiple and/or greater than a predetermined multiple of the ventricular sensitivity setting. The control circuit 80 may increase the ventricular sensitivity setting at block 438 and return to block 412. When the R-wave amplitude criterion is not met AT block 437, the control circuit 80 may return to block 412, not adjust ventricular sensitivity, but instead continue to switch to the test mode AT a predetermined frequency for accumulating oversensing evidence and adjust ventricular sensing control parameters as needed until the AT is no longer detected or the oversensing evidence counter is less than the "no oversensing" threshold (block 434), or greater than the oversensing threshold AT block 420, and the test is suspended (block 436 or block 422, respectively).

The techniques of flowchart 400 may be utilized during a detected AT episode to accumulate oversensing evidence when atrial rates are fast and/or irregular. When the AT is no longer detected, the control circuit 80 may switch back to accumulating evidence of oversensing in accordance with the techniques of fig. 7 or 8. Using the techniques disclosed herein, a medical device is able to detect and accumulate evidence of oversensing even when events are not actually oversensing or such oversensing events are ignored and do not interfere with ventricular pacing control.

These techniques improve the reliability of ventricular sensing and pacing performance of medical devices that perform the techniques, particularly when one or both ventricular sensing electrodes are positioned in close proximity or even in the atrioventricular. This may occur when ventricular pacing is delivered to the His-Purkinje system as depicted in fig. 1-3. Accumulation of oversensing evidence, including actual or potential oversensing evidence of atrial events and/or cardiac potential signals, may be useful for devices having or coupled to ventricular sensing electrodes that are in close proximity or in the atrioventricular chamber. When a ventricular pacing lead or electrode is positioned relatively low in or along a ventricle, e.g., for pacing the ventricular myocardium at the apex of the ventricle, one or both ventricular sensing electrodes are relatively far from the atrial chamber and the his bundle and bundle branch, making oversensing of atrial events and cardiac potential signals unlikely or unreliable. Subsequently, in such systems, it is unlikely that an oversensed atrial event or an oversensed cardiac potential signal will interfere with ventricular pacing control. Nonetheless, the techniques disclosed herein may be implemented in any medical device configured for ventricular sensing, such as controlling ventricular pacing and detecting ventricular arrhythmias and delivering ventricular arrhythmia therapy, when oversensing may interfere with proper device operation.

The following includes example techniques in accordance with aspects of the present disclosure.

Clause 1: a method, comprising: sensing a ventricular electrical signal; setting an R wave sensing threshold; receiving an atrial event signal; setting a post-atrial time interval in response to receiving the atrial event signal; generating an event time signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval; determining a count of event time signals in response to the generated event time signals; and adjusting the ventricular sensing control parameter based on the count of event time signals.

Clause 2: the method of clause 1, including: adjusting the ventricular sensing control parameter by enabling a post-atrial ventricular blanking period.

Clause 3: the method of clause 2, including: setting the post-atrial time interval and the post-atrial ventricular blanking period in response to receiving a next atrial event signal, the post-atrial time interval at least partially overlapping the post-atrial ventricular blanking period; generating a next event time signal without generating an R-wave sense event signal in response to the ventricular electrical signal being equal to or greater than the R-wave sense threshold during an overlapping portion of the post-atrial ventricular blanking period and the post-atrial time interval; and incrementing a count of event time intervals in response to the next event time signal.

Clause 4: the method of any of clauses 1-3, further comprising: determining a time interval from the atrial event signal to the event time signal; adjusting the ventricular sensing control parameter by adjusting an end time of a post-atrial ventricular blanking period based on the determined time interval.

Clause 5: the method of any of clauses 1-4, wherein adjusting the ventricular sensing control parameter comprises adjusting a ventricular sensitivity setting used to set the R-wave sensing threshold.

Clause 6: the method of clause 5, including: determining at least one amplitude metric from the ventricular electrical signal; and adjusting the ventricular sensitivity setting based on the at least one amplitude metric.

Clause 7: the method of clause 6, including: generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold; determining a peak amplitude associated with the R-wave sensed event signal from the ventricular electrical signal; determining the at least one amplitude metric based at least on the peak amplitude; and adjusting a ventricular sensitivity setting based on the R-wave amplitude metric.

Clause 8: the method of clause 7, including: determining an oversensing event amplitude associated with the event time signal from the ventricular electrical signal; determining the at least one amplitude metric by determining an oversensing event amplitude metric based at least on the oversensing event amplitude; and adjusting the ventricular sensitivity setting based on a comparison of the R-wave amplitude metric to at least one of the oversensing event amplitude and the ventricular sensitivity setting.

Clause 9: the method of any of clauses 1-8, including: adjusting the count of event time signals in response to not receiving the event time signals from the sensing circuit during a next post-atrial time interval; adjusting the ventricular sensing control parameter by disabling a post-atrial ventricular blanking period based on the adjusted count of the event time interval.

Clause 10: the method of any of clauses 1-9, further comprising: generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold; sensing an atrial electrical signal; detecting an atrial arrhythmia from the atrial electrical signal; determining that the R-wave sensed event signal was generated by the sensing circuitry during a post-atrial time interval; increasing a count of oversensing evidence in response to generating the R-wave sensed event signal during the post-atrial time interval; and enabling a post-atrial ventricular blanking period in response to the increased count of oversensing evidence.

Clause 11: the method of clause 10, wherein the control circuit is further configured to: determining an atrial event interval between two consecutive atrial event signals; setting an oversensing evidence criterion based on a ratio of the post-atrial time interval to the atrial event interval; comparing the count of oversensing evidence to the oversensing criteria; and enabling a post-atrial ventricular blanking period in response to the increased count of oversensing evidence satisfying the oversensing evidence criteria.

Clause 12: the method of any of clauses 1-11, further comprising: generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold; sensing an atrial electrical signal; detecting an atrial arrhythmia from the atrial electrical signal; temporarily disabling a post-atrial ventricular blanking period in response to detecting the atrial arrhythmia; determining that the R-wave sensed event signal was generated by the sensing circuitry outside of the post-atrial time interval when the post-atrial ventricular blanking period is temporarily disabled; and in response to generating at least the R-wave sensed event signal outside the post-atrial time interval when the post-atrial ventricular blanking period is disabled, disabling the post-atrial ventricular blanking period during the detected atrial tachyarrhythmia.

Clause 13: the method of any of clauses 1-12, including: generating an atrial pacing pulse; sensing an atrial electrical signal; generating a P-wave sensed event signal in response to the atrial electrical signal crossing a P-wave sensing threshold, receiving the atrial event signal associated with one of an atrial pacing pulse or a P-wave sensed event signal; setting the post-atrial time interval to a first duration in response to receiving the atrial event signal associated with a P-wave sensed event signal; and setting the post-atrial time interval to a second duration greater than the first duration in response to receiving the atrial event signal associated with the atrial pacing pulse.

Clause 14: the method of any of clauses 1-13, comprising: adjusting the ventricular sense control parameter by setting a safe pacing interval in response to the atrial event signal; generating an R-wave sensed event signal during the safe pacing interval in response to the ventricular electrical signal crossing the R-wave sensing threshold during the safe pacing interval; generating a ventricular pacing pulse upon expiration of the safe pacing interval in response to generating the R-wave sensed event signal during the safe pacing interval.

Clause 15: the method of any of clauses 1-14, further comprising: setting a post-atrial ventricular blanking period in response to the atrial event signal; and generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold outside of the post-atrial time interval and the post-atrial ventricular blanking period.

Clause 16: the method of any of clauses 1-15, comprising: comparing the count of event time signals to a first oversensing criterion when a post-atrial ventricular blanking period is enabled; comparing the count of event time signals to a second oversensing criterion different from the first oversensing criterion when the post-atrial ventricular blanking period is disabled; and adjusting the ventricular sense control parameter in response to the count of event time signals meeting one of the first oversensing criterion or the second oversensing criterion.

Clause 17: a non-transitory computer readable storage medium comprising a set of instructions that, when executed by control circuitry of a medical device, cause the medical device to: sensing a ventricular electrical signal; setting an R wave sensing threshold; receiving an atrial event signal; setting a post-atrial time interval in response to receiving the atrial event signal; generating an event time signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval; determining a count of event time signals in response to the generated event time signals; and adjusting the ventricular sensing control parameter based on the count of event time signals.

It will be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different order, may be added, merged, or omitted altogether (e.g., not all described acts or events may be required for performing the methods). Further, in some instances, acts or events may be performed concurrently, e.g., through multi-line processing, interrupt processing, or multiple processors, rather than sequentially. Additionally, although certain aspects of the disclosure are described as being performed by a single circuit or unit for clarity, it should be understood that the techniques of this disclosure may be performed by a combination of circuits or components associated with, for example, a medical device.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. The computer-readable medium may include a non-transitory computer-readable medium corresponding to a tangible medium such as a data storage medium (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

The instructions may be executed by one or more processors, such as one or more Digital Signal Processors (DSPs), general purpose microprocessors, Application Specific Integrated Circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, the term "processor," as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, the present techniques may be fully implemented in one or more circuits or logic elements.

Accordingly, a medical device has been presented in the foregoing description with reference to specific examples. It should be understood that the various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the figures. It should be appreciated that various modifications to the reference examples may be made without departing from the scope of the disclosure and the following claims.

Claims

1. A medical device, comprising:

a sensing circuit configured to:

sensing a ventricular electrical signal;

setting an R wave sensing threshold;

receiving an atrial event signal;

setting a post-atrial time interval in response to the atrial event signal; and

generating an event time signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial time interval; and

a control circuit configured to:

determining a count of event time signals generated by the sensing circuit; and

adjusting a ventricular sensing control parameter based on the count of event time signals.

2. The medical device of claim 1, wherein:

the control circuit is configured to adjust the ventricular sensing control parameter by enabling a post-atrial ventricular blanking period.

3. The medical device of claim 2, wherein:

the sensing circuit is configured to:

setting the post-atrial time interval and the post-atrial ventricular blanking period in response to receiving a next atrial event signal, the post-atrial time interval and the post-atrial ventricular blanking period at least partially overlapping;

generating a next event time signal without generating an R-wave sensed event signal in response to the ventricular electrical signal being equal to or greater than the R-wave sensing threshold during the post-atrial ventricular blanking period and the overlapping portion of the post-atrial time interval; and

the control circuit is configured to increase the count of event time intervals in response to the next event time signal.

4. The medical device of any one of claims 1-3, wherein the control circuit is configured to:

determining a time interval from the atrial event signal to the event time signal;

adjusting the ventricular sensing control parameter by adjusting an end time of a post-atrial ventricular blanking period based on the determined time interval.

5. The medical device of any one of claims 1-4, wherein the control circuit is configured to adjust the ventricular sensing control parameter by adjusting a ventricular sensitivity setting used to set the R-wave sensing threshold.

6. The medical device of claim 5, wherein the control circuit is configured to:

determining at least one amplitude metric from the ventricular electrical signal; and

adjusting the ventricular sensitivity setting based on the at least one amplitude metric.

7. The medical device of claim 6, wherein:

the sensing circuit is configured to:

generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold;

determining a peak amplitude associated with the R-wave sensed event signal from the ventricular electrical signal;

the control circuit is configured to:

determining the at least one amplitude metric based at least on the peak amplitude; and

adjusting the ventricular sensitivity setting based on the R-wave amplitude metric.

8. The medical device of claim 7, wherein:

the sensing circuit is configured to determine an oversensing event amplitude associated with the event time signal from the ventricular electrical signal;

the control circuit is configured to:

determining an oversensing event amplitude metric based at least on the oversensing event amplitude, the at least one amplitude metric; and

adjusting the ventricular sensitivity setting based on a comparison of the R-wave amplitude metric to at least one of the oversensing event amplitude and the ventricular sensitivity setting.

9. The medical device of any one of claims 1-8, wherein the control circuit is configured to:

adjusting the count of event time signals in response to not receiving the event time signals from the sensing circuit during a next post-atrial time interval;

adjusting the ventricular sensing control parameter by disabling a post-atrial ventricular blanking period based on the adjusted count of the event time interval.

10. The medical device of any one of claims 1-9, wherein:

the sensing circuit is configured to:

generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold; and

sensing an atrial electrical signal;

the control circuit is configured to:

detecting an atrial arrhythmia from the atrial electrical signal;

determining that the R-wave sensed event signal was generated by the sensing circuitry during a post-atrial time interval;

increasing a count of oversensing evidence in response to generating the R-wave sensed event signal during the post-atrial time interval; and

the atrial post-ventricular blanking period is enabled in response to the increased count of oversensing evidence.

11. The medical device of claim 10, wherein the control circuit is configured to:

determining an atrial event interval between two consecutive atrial event signals;

setting an oversensing evidence criterion based on a ratio of the post-atrial time interval to the atrial event interval;

comparing the count of oversensing evidence to an oversensing criterion; and

enabling the post-atrial ventricular blanking period in response to the increased count of oversensing evidence meeting the oversensing evidence criteria.

12. The medical device of any one of claims 1-11, wherein:

the sensing circuit is configured to:

sensing an atrial electrical signal;

the control circuit is configured to:

detecting an atrial arrhythmia from the atrial electrical signal;

temporarily disabling a post-atrial ventricular blanking period in response to detecting the atrial arrhythmia;

determining that an R-wave sensed event signal is generated by the sensing circuitry outside of the post-atrial time interval when the post-atrial ventricular blanking period is temporarily disabled; and

disabling the post-atrial ventricular blanking period during the detected atrial tachyarrhythmia in response to generating at least the R-wave sensed event signal outside the post-atrial time interval while the post-atrial ventricular blanking period is disabled.

13. The medical device of any one of claims 1-12, further comprising:

therapy delivery circuitry configured to generate atrial pacing pulses;

wherein the sensing circuit is configured to:

sensing an atrial electrical signal; and

generating a P-wave sensed event signal in response to the atrial electrical signal crossing a P-wave sensing threshold,

receive the atrial event signal associated with one of an atrial pacing pulse generated by the therapy delivery circuit or a P-wave sensed event signal generated by the sensing circuit;

setting the post-atrial time interval to a first duration in response to receiving the atrial event signal associated with a P-wave sensed event signal; and

in response to receiving the atrial event signal associated with an atrial pacing pulse, setting the post-atrial time interval to a second duration that is greater than the first duration.

14. The medical device of any one of claims 1-13, wherein:

the control circuit is configured to set a safe pacing interval to adjust the ventricular sensing control parameter in response to receiving an atrial event signal;

the sensing circuit is configured to generate an R-wave sensed event signal during the safe pacing interval in response to the ventricular electrical signal crossing the R-wave sensing threshold during the safe pacing interval;

the medical device further includes therapy delivery circuitry configured to generate a ventricular pacing pulse upon expiration of the safe pacing interval in response to generating the R-wave sensed event signal during the safe pacing interval.

15. The medical device of any one of claims 1-14, wherein the sensing circuit is configured to:

setting a post-atrial ventricular blanking period in response to the atrial event signal; and

generating an R-wave sensed event signal in response to the ventricular electrical signal crossing the R-wave sensing threshold during the post-atrial time interval and the post-atrial ventricular blanking period.

16. The apparatus of any of claims 1-15, wherein the control circuitry is further configured to:

comparing the count of event time signals to a first oversensing criterion when a post-atrial ventricular blanking period is enabled;

comparing the count of event time signals to a second oversensing criterion different from the first oversensing criterion when the post-atrial ventricular blanking period is disabled; and

adjusting the ventricular sense control parameter in response to the count of event time signals that meet one of the first oversensing criteria or the second oversensing criteria.